Being a teacher of Macs, I tend to install stuff like this on day one -- and while there are usually bugs to be ironed out later, I can honestly say that with the last two releases I didn't get bit by any of them, which means they were either fairly minor or fairly obscure (at least to me and my usage).
I *do* fully agree that a clone backup of the existing system is a really sound idea. Not that I think anybody "won't like it" but in case the install goes wrong.
As for worries about not liking it, a general reminder directed at nobody in particular: anytime anyone changes the visual aspects of something we are used to, there's an instinctual tendency to dislike. Giving oneself a little time to make a fuller judgement often results in a revised opinion.
From the impressions I've gotten from the various "reviews" of Lion I've read, a lot of visuals have changed, other aspects (like Mail and iCal) have been tweaked (rather than overhauled) and on the whole it sounds to me more like a refinement of Snow Leopard with some added iOS bits rather than any radical change. We'll see, obviously, but the fact that they kept the price low tells me that they didn't feel the need to overhaul the kernel or anything hugely different under the hood, rather they built on what Snow Leopard established.
