Sizes and items limitation for SharePoint List objects

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