Seriously High Memory Usage
I saw that there was a previously-closed issue on this, but at the moment PeepOpen is using almost 2 gigs of ram :)

I think we can agree that that has passed into the realm of absurdity :) This is with 1 large (> 5000 file) project and 3 much smaller ones. I know it's Ruby etc but that seems like a huge leak.
That is indeed quite a lot of RAM. I'm guessing that you're working with several projects at once, or is that a single project?
EDIT: You mentioned four total projects. I'll try to reproduce this situation and find a fix.
+1. I have the same issue. ~900 files, one project. After a day's use close to 2GB of ram.
EDIT: With MacVim
Same
Compare to the usage of RAM on drd's mac, mine is nothing. However I think I should mention it because before (Snow Leopard) PeepOpen usually took ~50MB of RAM for my project (a small one) and quite consistent (sometimes, it even decreased). Now with Lion, it starts up with ~60MB and keeps growing, probably to ~100MB. Seems unstable.
I confirm high memory usage with TextMate: 3300 files >100MB (file type icons, files metadata, animation, status bar -- switched off)