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.