As a new user to TextMate (and having been in involved in number of development projects), I can't help but bring the baggage of being used to certain performance, behaviors and expectations from a Mac application, so please forgive if I come off a bit frustrated.
I was pretty frustrated myself when I switched to OS X (over the general sluggishness), and I'm a tad irritated by the many hoops I have to go through, to get decent performance on low-end system (which seems to be most below a 2.5 GHz G5 with AGPx8 ;) ).
But OTOH I've also changed my view on these things, make it work, then make it fast, I think that's what Apple does, and it's a philosophy I've adopted myself -- TM is far more dynamic than any other text editor, and makes much more use of “declarative” rules than code/plugins, and I think that adds tremendous value, despite the overhead these things bring.