I didn't get the original message, so I'm replying to this one. Apologies for that.
But then when should it update the project drawer? You can create a static (thus non-updating) project by dragging files (instead of folders) to the project drawer. If you want to add an entire folder structure as a project you can e.g. create a script as the one attached below, which takes a folder as first argument and writes a tmproj file to stdout. I didn't make it handle special filenames though (like containing quotes).
I'm seeing the same problem with my projects - updating the project drawers takes a few seconds. This is especially annoying when I switch between TextMate and the Web browser in very short sequences.
First I also thought about a setting or even a manual update. But my suggestion now would be to do the project refreshing in a separate thread in the background. Is that possible?