Sizing of dbs, sites, list and more objects in Sharepoint

File Name, Length, Size and Invalid Character Restrictions and Recommendations
http://blogs.msdn.com/joelo/archive/2007/06/27/file-name-length-size-and-invalid-character-restrictions-and-recommendations.aspx

Plan for software boundaries
http://technet2.microsoft.com/Office/en-us/library/6a13cd9f-4b44-40d6-85aa-c70a8e5c34fe1033.mspx

Plan enterprise content storage
http://technet2.microsoft.com/Office/en-us/library/9994b57f-fef8-44e7-9bf9-ca620ce207341033.mspx