SharePoint 2010 limitations are listed here: http://technet.microsoft.com/en-us/library/cc262787.aspx
How many items in a list?
How many document in a folder?
How many sites per sitecollection?
Sharepoint 2007 have some limitations regarding recommended maximum of elements in a list, documents per folder, fields per list and so on.
These limitations (or guidelines at least) are listede here.
The issue have been adressed in Sharepoint 2010 that supports large lists. View more on Large List Support here
Note! On a document library where version limit hasn’t been set: If you have a document with, lets say 10 versions and suddenly set the limit to 5, the excessive versions arent deleted instantly but only when you edit the document later.
1. Document1 has 10 versions (1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0)
2. You set the versions limit (Optionally limit the number of versions to retain) to 3. Document1 still has 10 versions
3. You edit Document1
4. Document1 now has these versions (7.0, 8.0, 9.0, 10.0). Versions (1.0, 2.0, 3.0, 4.0, 5.0, 6.0 are permanently deleted – they are not in any of the trashcans)