Grep for something, excluding the annoying svn metadata (.svn**)
The find piece could also be used for more general tasks -- just remove the pipe and take a look at the output to see if it will work for you.
I tried (and failed) to use the find to a path preserving copy from within a subdirectory in a checkout...though there must be a way.

find . -path '*/.svn' -prune -o -type f -print | xargs -e grep -I -n -e PATTERN

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:

!.*/(\.[^/]*|CVS|vendor/rails|_darcs|\{arch\}|blib|.*~\.nib|.*\.(framework|app|pbproj|pbxproj|xcode(proj)?|bundle))$$

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.