To play with it of course! That is why I bought one.
That's actually what was getting me to consider buying one as well... I've always kind of wanted to play with Android, and my old Windows Mobile phone (AT&T Tilt) has Android on it now, but it's... well, kind of slow :\. I think it takes around 3-4x as long as my iPhone just to boot.
I think what makes me a bit reserved about buying one is just that there are some apps I'd prefer to use on a tablet instead of my phone, but I'd need an iPad currently for that. So instead of paying $200 (+ this warranty that everyone says to get) for this, I could put that toward an iPad (which the newer revision should be unveiled tomorrow too).
I guess I'd just be worried that... similar to a lot of things, the Nook Color, even when rooted, would just be mostly unused... kind of like my EeePC netbook that I've got in my drawer here

. I also think having a good Honeycomb build would interest me a lot more as well... I was actually rather interested in the UI while reading the Xoom review.