I've also been looking at IE8, first beta 2, then RC1.
RC1 is a HUGE improvement over Beta 2, but still nowhere near a finished product. I think the way it's all 'shiny' and enticing on Microsoft's website is designed to trick unsuspecting users into installing it, to be honest.
As with the other warnings, DO NOT install this on your main PC, unless you know what you're doing. If you do, be prepared to accept that it doesn't work properly yet, so have another browser installed, just in case!