I'm so happy, just submitted a new app yesterday.
The client side that runs on the iPhone is written completely in Objective-C. Binary size is 200k after compression, and the app is multithreading / multicore ready. I used grand central dispatch (GCD) whenever possible, so the UI thread is never blocked and the background tasks can work like crazy.
Server side is in Haskell, which gives me extremely rapid development cycle and robust design. I spent only 2 days on the server code, yeah, 2 days...
From my own usage, this solution is so fast that I don't even believe it.
Core technology used:
I like how all the pieces are tuned to work together seamlessly to provide a complete solution. Will talk more about this when the app is online.
BTW, I'm learning Boo! This is going to be fun!!!