Norton products are awful. They won't integrate with other Norton products without blowing up... they won't upgrade to newer Norton product versions without blowing up... every Symantec knowledgebase article invariably leads to 'uninstall/reinstall', which is usually the reason you are there (because an uninstall failed, or the initial install failed)... and as previously mentioned, the removal tools don't remove everything (I'm not too far away from making my own, argh) and leave you unable to reinstall... it's pathetic. Then there's liveupdate which makes you update 30 times in a row, rebooting each iteration. Why can't there be a rollup? Why can't the 200x version be up to date for once? Right when NAV 2005 came out, there's 963,440,721 MB of updates for it. What gives? Norton Corporate is OK though; it doesn't have *as many* problems.
On the other hand, McAfee Antivirus/Security Center crashes a lot and is very obtrusive (popup windows more obtrusive than XP notify balloons, asking you if you want to continue what you were doing or be annoyed some more - both answers lead to annoyed some more)
So that's the main two.. then there's all these runner ups, half of which nobody's heard of, or they are brand new to the scene.. claiming to get all viruses. Well, they all suck. I have Norton Corporate Edition (which is half decent), and I only use it because other users are on my machine that make starfish mistakes. I personally never get infected with viruses or spyware.