Ok, i've tried three. My bias as a reviewer is that I use and like Beersmith as my primary database. I'm looking for an app that i can import & export between the two, and for a brew day calculator that feeds off the recipe.
BrewR demo - Allows you to put in recipes and run a brew day timer. At the moment you can't import beer.xml files - but the developer is working on this. Doesn't have a calculator for all those brewing conversions, etc
HomeBrew Calculator - This has all the calculations - attenuation, srm, yeast pitching, hop bitterness - and a boil timer. But no recipe database. At the moment i'm using this for the timer.
Brewzor Pro Beta - This is the best of the three apps, but doesn't have a boil timer. Can import xml files, so it was simple to update with my beersmith recipes. Brewing calculators, including refractometer, yeast pitching rates, etc, shopping list generated from a recipe.
I confess I haven't gone beyond a cursory view of most of these yet.