It's in private alpha/beta/gamma/whatever right now (has some rough edges to clean up), but is more or less functionally complete and pretty stable.
I'm a big fan of the Seinfeld calendar, and have seen other services which do similar things but were unsatisfying to use, either from an aesthetic or functional perspective. Streak.ly is designed to be simple, good-looking, fast, fun, (and hopefully addictive). (FWIW, it's also a place to experiment with user stickiness stuff I can potentially roll back in to Forrst.)
There are also some in-progress social/game/motivational features I plan to roll out in the next few weeks that hopefully contribute to the enjoyment factor of the app.
Streak.ly uses Twitter for authentication, and I've set up a URL to let HN folks in early: http://streak.ly/auth/twitter/start?secret=showhn
I'd love any and all feedback and/or criticism you may have.
Thanks!