NS6 looks nice, which means loads of people prbably use it!
I've always found NS 4.7/4.8 to be a little unstable, and one hell of a resource hog, the programmers at netscape seem to have forgotten about releasing mempory when you are finished with it.
NS doesn't like to display default font very nicely, unless of course you have super vision. It always like to display text just that bit smaller. Not a problem if you are aware of it, but not everybody is. I know I have to drum it into all the new designers we take on, cos I get fed up of having to sort it out myself.
CSS implementation in 4.7/8 is crap, and is far better in IE. (Note I said better, not good) Haven't really tested it in NS6, I de-installed the piece of sh*t before I got that far! ;-)
Consistency. The guys at netscape don't seem consistent. I can't remember what the problem was, but the boss, myself and another techie were looking into a complaint from one of our customers that the site wasn't being displayed properly. It turned out that, the designers had tested the site on 4.08 and it was fine, but 4.7/8 didn't support an old standard feature. (Sorry it's vague, but I can't remember the problem at this very moment).
DHTML support in NS is way behind that of IE. Again, let's not judge them on good or bad (or standards for that matter), IE is just better at it.
IE has better integration of third party plugins.
And I just generally find that things look better in IE.
On the subject of OS integration, I've never really had a problem with it. In fact if anything I'd say the MS IE/OS integration's problem isn't that it's forced on you, I'd say it's that it's not very good. KDE does it better. Click on an html file in the system browser and voila it's displayed, no need to load another prog. MS's active desktop is a waste of time, and needs better implementation. It's good(ish) idea, it's just not very well done.
If I could move away from MS products I would, I love linux. I spend most of my day in an SSH terminal on my servers. MS might be evil but a big company with that much money can't produce all bad products (statistically speaking). Some of the products that role out have to be good. And I think IE is one of them.
Of course most of the problems, are due to the fact that most thigs get developed for MSWin. It is the most popular OS. I think if we are ever to win the Linux/Win war we need not to be developing progs that just run on Linux. We need to dual develop and fight them on their own turf. Sort of like NS, and Star Office (or whatever it's called these days), but better. Two good ideas, just not very well implemented. And in Star Office's case I'm being very nice and polite here. :-)
And of course I play games, so I have to use win.
Ok so this is not only off topic, but it's turning into two topics!!!
( I hope this little discussion doesn't tarnish your opinion of me and stop you answering any PHP questions when I post them! )