Hi,
yes I'm actually still on prehistoric KM1.6 due to my online machine being win98
No I do not change my UserAgent (=how the browser identifies itself to websites, it may be faked) normally, only when a website is stubborn with old browsers
Yes faking the UA-tag helps very often, although not always. More and more often nowadays I need to kill the css-style to get access to more content - but hey, only rarely do I see such a nasty "old browser" warning, and all-around for this *extremely* old mozilla engine that's absolutely amazing in todays web!
So I'd say, with the rather current mozilla engine in KM75, that should still be good for awhile, even when Dorian will certainly run out of spare time again some day. The break between KM1.6 and KM74 has been very long, so long that most KM fans had already feared the browser was already dead, but then Dorian showed up again in autumn 2013 and has been working very hard ever since to update KM to a modern engine again, and finally KM75 is about ready for publishing.
But most of those "old browser" warnings really require nothing but a faked UA name tag to fool nasty servers, because the content itself still works fine in 99%. A more difficult subject is security though, due to older mozilla engines (gecko)...