I'll echo the other comments here.

Obj-C is refreshing compared to C++. It'll take you about 2-3 hours to get a handle on it. (Granted, I like C# and Java better, but for Mac development you are better off with Obj-C.)

The currency converter app is a reasonably good tutorial. Go through the Hillegass book. It's valuable.

Learn bindings. I'm still trying to get my head around them. As Thinine pointed out they are VERY powerful. (I'm currently exploring CoreData .... something else that we don't have anything similar to in Windows ... ADO.NET is great, but this seems to be better thought out.)

Welcome to the club.