Sharepoint 2007 limits overview

When setting up Sharepoint 2007 or creating custom stuff for Sharepoint, please take a look at this:

• Detailed Sharepoint limits overview
• Plan for software boundaries (detail overview of limitations, performance tips, ....)
  Also notice that there are also limitations for security principles:
  "Security principal: max 2,000 per Web site. The size of the access control list is limited to a few thousand security principals (users and groups in the Web site)."