I'm a (classic) MacOS developer making the (rather painful) switch to MacOS X. I've got around 9 years experience developing with C++. I'm really comfy with C++, the standard C++ library (with the ultra-nice STL) and various compilers, frameworks and APIs. I consider myself an extremely good C++ developer. I gained all my C++ skills through self study, practice (of course) and by using the tremendous C++ resources out there: from other C++ developers, the host of C++ books that have been published over the years, and various other places like web-sites and mailing lists.
What scares me about Objective C is that the infrastructure behind it is lacking. There aren't any (AFAIK) currently published Objective C books out. No C++ books aimed at beginners, no reference manuals, no excellent GURU books like Effective C++ and More Effective C++. There aren't many good Objective C tutorial web-sites around, I haven't found a Objective C FAQ anywhere and I have yet to be introduced to a programmer in the workplace with Objective C on his resume.
This makes it hard if not impossible to gain the Objective C skills needed to develop commercial software. I'm hoping as Apple forces Objective C and Cocoa down the throats of Mac developers worldwide all these resources will begin to appear.
Until then I'm sticking with C++, my nice C++ frameworks and a good C++ compiler.
Update: Sept. 23 2002. Objective-C is (and has been for over a year) been my language of choice for Mac OS X development and I'm working on a couple of pieces of shareware in Cocoa. Go figure!