SharePoint 2010 boundaries and limits of Microsoft SharePoint Server 2010

SharePoint 2010 supports:
300 content databases per web application
250,000 site collection per web application.
10 application pools per web server.
Size of content database can be 200GB.
In case of document archive scenario there is no limit on content database size.
There can be 60 million items including documents and list items in Content database.
SharePoint 2010 recommennded 2000 site collections per content database, but that can be maximum of 5000 site collections.
SharePoint 2010 supports 250,000 web sites for site collection.
List row size can be 8,000 bytes
File size in a list or library can be 2GB.

You can store 30,000,000 documents per library.
400,000 major versions are supported in library.

There can be 30,000,000 items in a list.
SharePoint 2010 supports 25 web parts per web part page.
There can be 2 million users in a site collection.
There can be 5000 users in a SharePoint group.
There can be 10,000 SharePoint groups per site collection.
2,000,000 user profiles per service application.
There can be 500,000,000  social tags, notes and ratings per social database.
5,000 blog posts per site.
Can be 1000 comments per post.

You can follow this link for more details.