If you have a rails project you load up in textmate, and you have some version of Rails in vendor/rails, you probably know that doing a 'find in project' takes a lot longer because it scans all the rails source files. You also get a lot more crap to wade thru when doing a go-to type (command t). To exclude vendor rails, click on the project root in the drawer, click on the "i" icon, and change the folder pattern to this:
Note the addition of "vendor/rails" to the regex. You can also add this to preferences -> advanced to make it the default for new text mate projects.