I posted this to textmate-dev a few days back, but it seems that list is mostly for SVN announcements, so I'm re-posting.
I figured out a way to approximate snippet-power templates: http://henrik.nyh.se/2007/02/27/snippet-power-templates-in-textmate/
It's not perfect, but I think it's pretty cool. Any feedback/improvements is very welcome.
Since the announcement on textmate-dev, the blog post's been updated with a new solution that is quite a lot better.