So I created a separate partition on my drive and downloaded and installed it. First impression? Meh. I don't hate the new UI like so many are complaining about, but I'm also in no hurry to rush out and make it my daily driver. Of course I will when it's officially released, but right now I see nothing compelling enough to jump wholeheartedly into the beta program and put my data at risk. (Remember, I learned that lesson—unfortunately multiple times—in the past.)
I will say, however, that for the first developer beta of a new O/S, it seems incredibly stable compared to times past. For the few hours I was playing with it nothing locked up, nothing crashed…but admittedly I wasn't doing any of my usual tasks since none of my daily applications were installed.
I'll also say that I rather like the new wallpaper, as trivial as that may seem. I snagged it to use with my existing Sequoia installation.