If you need to handle a large amount of data, this article will be very handful.
First thing to keep in mind is the SharePoint Boundaries and Limits (http://technet.microsoft.com/en-us/library/cc262787.aspx) and this article Designing large lists and maximizing list
performance 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?
That happens because the SQL Server limit of row locks. When you try to perform a operation to up 5,000 items, it's easier to SQL to do a Lock Scalation and temporary lock the entire table. When this happens very often, the users will experience a performance
degradation. (For more info, see:
http://office.microsoft.com/en-us/sharepoint-foundation-help/manage-lists-and-libraries-with-many-items-HA010377496.aspx).