The templating system they developed looks pretty sweet http://github.com/facebook/tornado/blob/master/tornado/templ....
Just played around with it a bit and it's basically what I want:
1) Simple and clear syntax (e.g. they use 'end' not endfor, endblock, etc)
2) Assign template variables to anything (including functions)
3) Don't over-restrict the author (e.g. they allow list comprehensions in if tags)
4) Block and extends statements.
Error handling seems to be a little clearer than other template languages though still not great:
Clearly it's not going to be for everyone but after slogging around with Mako for the last year (<%namespace:def /> tags anyone?) this is like a breath of fresh air.