I used it for the last month or so, and I like the UI, but I just recently switched to Brewersfriend. I wanted an app/webpage that would integrate with my Tilt, and the Brewersfriend software seems to be the way to go, for me. I dropped Beersmith as well, which I'm still trying to figure out if that was the best move.
That said, if I was sticking with Beersmith, I'd keep using Brewstat.us. Its really easy to upload your recipe into it and track fermentation/temp through the Tilt.