I've done about 60. Roughly 3 evolutions in a minute. Theorectically can do about 90 but I estimate 70-80 is more likely. There are 3 things I know that can influence how many you get to evolve in the 30 mins:
1. Whether you have seen the evolutions before. If you don't have the evolutions in your pokedex, then you will also get the pokedex entry animation when you evolve it. That will take up some time though. However, that's nicely compensated since you get the 500XP from seeing a new pokemon which at double becomes 1000XP.
2. How you order your list. If your list is haphazard and not ordered properly, you can end up wasting time checking to see which pokemon can evolve and looking for them. I recommend ordering by #Number and transferring all unneeded pokemon.
3. How fast your device is. I've read that force closing the app and restarting it can take about 8 seconds which is faster than waiting for the animation to finish. Haven't tested it yet but planning to do so soon.

Damn good eh you. So far max i evolve is bout 67 >.<