Objective-C is not all that bad...
I'm a Java Web developer, without any real experience on desktop programming. But recently I was given the chance to do a small iPhone app for one of our clients, so I had to learn Objective-C from scratch to do it.
Objective-C might seem a little weird at first, but when you got used to the sintax the concepts used on the frameworks are not all that different from the Java counterparts. Appkit for example is much more pleasant to work with than Swing, for example.
It took around a week to learn the Objective-C basics, and another week to build a fairly complete prototype of the application.
So while might be a barrier for Java developers, it's not that high.