SharePoint Large List Performance

No matter how big or small, lists and libraries are vital to your use of SharePoint 2010 in many ways. But when a list or library has a large number of items, you need to carefully plan, organize, and account for how data is accessed. By planning and using key list and library features, you can ensure that you and other users quickly find information without adversely affecting the performance of the rest of your site.

http://office.microsoft.com/en-us/office365-sharepoint-online-enterprise-help/manage-lists-and-libraries-with-many-items-HA101967267.aspx


Designing large lists and maximizing list performance (SharePoint Server 2010)
http://technet.microsoft.com/en-us/library/cc262813.aspx


According to SharePoint Boundaries and Limits, it's supported 30,000,000 items per list. That's a lot of information.

So, Why the 5,000 items limit?
http://office.microsoft.com/en-us/office365-sharepoint-online-enterprise-help/manage-lists-and-libraries-with-many-items-HA101967267.aspx#_Toc268535094