I've Flashed this 'unofficial' update and the results have so far have been good: The lag is virtually gone; everything loads/runs smoother (particularly things with lists, ie. Contacts/SMS/pics/etc); Market loads, scrolls, and downloads much faster; the keyboard is more responsive and accurate (no more "hiccups" or missed letters while typing); GPS/compass fixed; and a whole slew of other minor improvements.
It's a promising update, and a great indication of what this phone is really capable of. I can't wait for 2.2.