Maybe it's because I'm a librarian, but I really liked the category feature in iBlog. It made assigning and organizing categories to be very easy. iBlog also generates an RSS feed - which is essential for blogging software, I think.
I do have two negative things to say about iBlog. The first thing is that although I like its news aggregator, it provides no simple one-click method of posting items from the news aggregator to the blog. Radio Userland does this - and I thought that was the whole point of having blogging software integrated with a news reader. It is very likely that this omission will be fixed in future releases of iBlog, so this is not a huge problem.
My other concern is more of a social rather than a technological issue, but it's real and is the major reason why I don't switch to iBlog tonight. It's that iBlog is so relatively new and has not yet established a community of users. I've talked about blogging communities before (see Digression2). Although I think one's blogging software is a very loose and less significant community, it does count for something. Maybe it's also because most of the time I feel quite at home in the Salon blog community.
Anyway, I'll finish by recommending iBlog to anyone starting a new blog on a Mac (OS 10.2). Because it's on a Mac and the software is very Mac-like, you won't waste as much time figuring out the technology and can spend more time being creative.