The situation with Monotouch has changed in the last few weeks. On May 2nd, all the Monotouch and Monodroid developers were laid off, including Miguel de Icaza. He documents what happened in this blog post. He and the other MonoTouch developers started a new company Xamarin, however as they don't own the MonoTouch code they will probably have to start from scratch with it.
Since Novell (who is owned by The Attachmate Group) hasn't seemed to have hired anyone to replace them (and I don't see how they could hire the anyone to match the talent they got rid of), I don't believe you will get very good support continuing to use MonoTouch. Even their website (monotouch.net) isn't loading for me. So I can't see any way to justify paying $400 for a product that now appears dead.
So while it was a really nice platform to work with, I would hold off using it and either wait for the Xamarin guys to produce their framework, or to just use the apple tools.