When you rename the user in Active Directly you might find that the old name is still resolving in People Picker when granting that user permissions. This is happening because user's entries for granted permissions are stored in a hidden “User Information List”  located at http://<SiteCollectionUrl>/_catalogs/users/detail.aspx. And if the same user was added before his/her name wont be updated with the new changes from AD (even after running a full or incremental import via UPS).

One of the approaches to provide high availability of SharePoint 2010 is using Log Shipping for service databases. However, SharePoint 2010 does not support log shipping for all databases. Such databases as:

Activating AD synchronization should be considered a long-term commitment to coexistence. You cannot currently deactivate directory synchronization. Once you have activated directory synchronization, you can only edit synchronized objects using on-premises applications.

SharePoint does not allow deleting a content type from a list if that list contains items of that content type.However, Microsoft SharePoint Foundation 2010 and SharePoint Server 2010 have different behavior for deleting content types:

When multiple crawl databases exist, an Crawler distributes results evenly across database, however if we have odd number of cralwed hosts the decision is based on the # of items\doc id’s are stored in the Crawl DB.

 
Planning of backup & restore process becomes very critical when you are handling the large content volume in SharePoint 2010 due to some of the limitations of the content backup and performance issues. Let's say you have the terabytes of data in your SharePoint 2010 Farm and you create the backup/restore policy.

When the new content is added to the SharePoint Farm 2010 the indexing is starting. The feed performance is mainly determined by the configured number of item processing components. Both the number of the CPU cores and the speed of each of them affects the results.

The following table represent the recommended SQL Server RAM for the SharePoint 2010 environments:

Sometimes you might be in the situation when you accidentally deleted your SharePoint site from IIS. It's not a disaster, because nothing happened to your site, except you lost the access.

Using SharePoint 2007 on Windows Server 2008 might bring additional steps to configuration that didn't exist in Windows Server 2003. On of the most questioned area is "why I can't save Office Document to the SharePoint Library"?

The Stsadm command-line tool of SharePoint 2007 has the following limitations: As part of a farm backup, backs up, but cannot be used to restore the configuration database or Central Administration content database. For more information, see Recovering the configuration database and Central Administration content database. Site collection backups affect performance, and they can cause access errors. They should only be used when the site collection is locked. Site collection backups can be slow when working with collections larger than 15 GB. We recommend that you use database backups if you are working with site collections larger than 15 GB. Note:  
If you want to individually back up a site collection that is larger than 15 GB, we recommend that you move it to its own database, and then use a database backup. Source

SharePoint 2010 doesn't allow you to install the "Complete" mode on non-domain local user accounts by default, because it's considered as "Development" environment and you should install in "Single Server" mode.

When you test you SharePoint perfomance make sure that you are using the right testing data.

User Profile is one of the SharePoint features, which provides searching across your users and surfacing user's info across your organization. Such scenario is very common in intranet scenarios.

It is important to realize that SharePoint stores a complete binary copy of every version of your document in the SQL Server database.

If you want your Index server to crawl a particular WFE, leave the default setting alone and modify the HOSTS file yourself. This way you can direct it to hit one server for some sites and another for others.

Be careful when you try to import sub-site to be your root site, especially when you have publishing sites. STSADM import/export doesn't work doesn’t work too well when you export a sub-site and import it to the top level site in a site collection.

SharePoint 2008 Service Pack 2 provides new feature called "read-only" database - when a content database is marked as read-only via SQL Server, the user interface will be modified so users cannot perform tasks that require writing to the database.

Office SharePoint Server 2007 does not support crawling content on sites that have logon pages that contains a series of forms that span multiple pages (wizard-based forms), or forms that use dynamic content rendered.

SharePoint crawling options provide the "Crawl complex URL" option, that applicable on the site with URL that contain a query parameter specified with a question mark (for example, www.mysite.com/list.aspx?item=1). Depending upon the site, these URLs might or might not include relevant content.

SharePoint provides you "Export to Spreadsheet" feature across almost all list, allowing you to export your list content to Excel. But not all lists have such functionality. For example, this option is not available for User list.

Almost all changes that developers and administrators introduce to SharePoint are completed via “jobs” mechanism of SharePoint (Central Administration –> Operations --> Timer Job Definitions). Your changes are queued and SharePoint complete them when “job” time comes.  It might be a bit frustrating, because all jobs have different timing and SharePoint doesn’t provide you UI to change when jobs start.

Virtualizied environment is very common for SharePoint farm. One of the most important factor of such farms is optimization that differs slightly from optimization of the physical environment . But firstly, we need to know how good our farm operates, measuring different parameters, before trying optimized it.

SharePoint Site Template has one very handy feature – it can be registered inside a Site or you can restrict certain sites to use only certain templates.

Sometimes, you may find that you get “HTTP 400 Bad Request” error, or “HTTP 401.1 - Unauthorized: Logon Failed” error when navigate to local SharePoint sites and asked for credentials tree times.

Historically, SharePoint 2007 provides a nice feature called Explorer View (came from 2003 version) that simplifies document management - like upload, delete, and copy items across different Document library, using drag-and-drop feature.

SharePoint provides you two approaches to design and deploy WorkFlows - via SharePoint Designer(SPD) and using Visual Studio. But you should be aware that deployment of WorkFlows has some differences in the security model that might cause you permissions issues.

Working of migration of SPS to MOSS 2007 in these days and would like to share my experience about number of small tricks, which really annoy you if you don’t know them, and which could save hours during your next migration