I haven't had much use for Tapbots' Weightbot, even though I actually am currently watching my weight, but I really appreciate the look and feel of the program -- it's one of the most polished apps on the App Store. And Convertbot is no different -- while the actual situations where I need to convert units are pretty few and far between, the app is just so intuitive and polished that you look for ways to use it, from the stylistic user interface to the little beeps and clinks that make the buttons feel as tactile as they can on the iPhone's touchscreen.
And now there's even more opportunities to use the app: with the newest version 1.1, out now in the App Store, you can convert more than 100 different units, everything from angles to lengths to cooking volumes to even speed, time, and work (I can't remember the last time I had to convert BTUs to Joules -- high school? -- but this app can do it).
At just 99 cents, it's definitely worth trying out, if you're a fan of quality iPhone apps at all. I kind of wish Tapbots would aim a little higher, but then again, this is kind of their thing: taking really simple apps and polishing the heck out of them until they shine way past their basic functions. It would be interesting, though, to see what they could do with a bigger concept.