Seems to insert 4 spaces always. I've got mine at 2 spaces and I like it that way!
Confirmed: this is a known issue. I'll fix it when I figure out how to ;) If anyone knows which direction to take (to find out in a TextMate command how many spaces should be in a tab), let me know or feel free to fork and fix it.
Edit: Hmm, I think it's TM_TAB_SIZE. I'll try to hack around a fix soon.
These values are passed as command-line parameters? Perhaps the vim plugin can make use of this, too.
If I remember right, the VIM plugin now respects shiftwidth. It's the TextMate support that was lagging behind.
To be fixed in v0.2
Fixed in v0.2.