You can count me as one who downloaded it and doesn't know what the hell they're doing. I've just been using some of the example projects Apple made available to try to teach myself. It's not going well, and all the Objective C resources I've found seem to expect you to already know C :-/
No surprise that an SDK would have as it's target audience software developers.
If you do want to learn it's best to start by writing some programs that run on the Mac. It is always easier to write software for a large powerful machine than for a small device. Easier by a large factor. "C" is easy to learn. You can be up to speed in a week. The language itself is so simple. What takes times to learn is the libraries and frameworks that you use. Those are huge and there is a ton of stuff to read. When it comes right down to it the programming language is really a kind of "glue" that you use to string together calls into the framework libraries.