Anyone Own/Use A Robotic Lawnmower?

Toying with the idea of getting a basic model (something like a Robomow rm510)...For one, I like my Roomba cleaning my house, 2) kinda' getting a little lazy now, and 3) well, I just like robots in general.... Any comments, caveats or advice from anyone who has any experience with them? Yes, I do realize I could build one as well... just an option...