At some point you may want to do an Enterprise Search query and specify that the results come from a particular content source.  A lot of times you might create a custom scope with that content source in it, but if you don't want to create a new scope, you can just query the content source directly.  The syntax is simple.  Just use it like in the example below.

ContentSource:"Local Office SharePoint Sites"

In this case, I want everything to come from the Local Office SharePoint Sites content source.  You can of course combine it with other terms as well like in the example below.

Bike Color:"Red" ContentSource:"BDC AdventureWorks"

In this case, it would search for red bikes in the BDC AdventureWorks content source.  Kind of a simple tip today, but I really haven't seen this documented anywhere.