Thanks to Mark Harrison i have used his guidelines for the SharePoint limitations. I am just publishing his content again here in my blog for my reference.
Site collections (Database scope) 50,000 Total throughput degrades as the number of site collections increases.
Web sites (Web site scope) 2,000 The interface for enumerating sub sites of a given Web site does not perform well much
beyond 2,000 sub sites.
Web sites (Site collection) 250,000 – You can create a very large total number of Web sites by nesting the sub sites.
Documents (Folder scope) 2,000 The interfaces for enumerating documents in a folder do not perform well beyond a thousand entries.
Documents (Library scope) 2 million You can create very large document libraries by nesting folders.
Security principals (Web site scope) 2,000 The size of the access control list is limited to a few thousand security principals, in other words users and groups in the Web site.
Users ( Web site scope) 2 million You can add millions of people to your Web site by using Microsoft Windows security groups to manage security instead of using individual users.
Items (List scope) 2,000 The interface for enumerating list items does not perform well beyond a few thousand items.
Web Parts (Page scope) 100 Pages with more than 100 Web Parts are slow to render.
Web Part personalization (Page scope) 10,000 Pages with more than a few thousand user personalization are slow to render.
Lists (Web site scope) 2,000 The interface for enumerating lists and libraries in a Web site does not perform well beyond a few thousand entries.
Document size (File scope) 50 MB The file save performance degrades as the file size grows. The default maximum is 50 MB. This maximum is enforced by the system, but you can change it to any value up to 2 GB (2047 MB) if you have applied Windows SharePoint Services Service Pack 1.