Below are recommended guidelines for creating total # of site collection, webs, document library and many more …
1. Recommended limitation for SharePoint site objects
http://technet.microsoft.com/en-us/library/cc287790.aspx
2. Limitation guidelines for SharePoint 2003 and SharePoint 2007
http://www.sperto.com.ar/fs_files/user_img/articulos/SharePoint%20Limits.pdf
Apart from this article discussion, here is very good link which will describes logical architecture of site collection.
http://www.sharepointblogs.com/llowevad/archive/2007/06/25/site-collection-logical-architecture.aspx
Filed under: SharePoint Admin, SharePoint Architecture, SharePoint List, SharePoint Object Model | Tagged: Document library, logical architecture of site collection, MOSS, SharePoint, SharePoint List, SharePoint Object Model, SharePoint site objects, Sizes and items limitation for SharePoint List objects, SPListItem, total no of site collection