The Lab has a ‘Second Life LIMITS’ page in the wiki. It is a handy reference for a number of things. I missed that in December 2012 the page was getting revisions and has been for a time. The page has had a number of updates and new information added.
This is a page editable by the community. In December Perrie Juran made some changes. In November Ibrew Meads, Kireji Haiku, Darien Caldwell, Uccello Poultry, and Stickman Ingmann were making changes. If you look through the page’s history there are some well known names contributing to the Wiki.
People discover limits now and then. I found that recently people have discovered you can only have 10,000 items in an inventory folder. That is a per folder limit. I can’t imagine anyone having 10k items in a single folder. But, I assume someone did.
BTW, the excess items are not lost. You just cannot see them in the folder. Move some out and others become viewable.
This is a must-know-about page for Second Life™ builders.