I tried to do a search on this before just starting a new post and this appeared to be the most relevant, so I'm resurrecting it.
I haven't came across an iPhone brewing app that's convinced me enough to spend money on. If it wasn't for the some of the reviews for Brew Pal, I would totally try it being just a $1 (I'd prefer to wait for his 2.0 version before I would buy based on his website and the reviews in the App Store). I use to have some pretty good free ones on my Droid before I switched to the iPhone 4S. Now that I recently bought the 2.0 for Mac, I certainly agree that it would be nice to have an iPhone app that works with the software on my computer. It probably wouldn't be a bad idea to have an standalone app of Beersmith with most of the functions that the computer version offers, but a separate one tailored for current computer-based Beersmith users would be nice too. A portable version that can sync the two together (in both directions) would be quite handy. I'd pay a $1 for an accompanying, complimentary one. I don't own an iPad at this time, but that certainly sounds like a good option to have as well.
Just wanted to share my interest for one too.