Honda (Europe) joined this growing market last year with the Miimo robotic mower and the two models they offered rated high in some independent testing.
Honda (USA) is evaluating the Miimo for the USA market; no word yet if it will be sold here or not. We are testing one here at the Honda office were I work in Georgia, and it seems to do a decent job on slopes. We have fescue turf, and Miimo dutifully motors out of the charging dock each day and trims the grass.
If you are a big fan of ultimate, manicured, striped baseball field look, a robo-mower is not for you. They tend to be very random in mowing patterns, and a freshly trimmer lawn can look a little fractal-ly sometimes.
Miimo Demo at The Honda Classic
-Robert@Honda
Caveat: I work for Honda, but the preceding is my opinion alone.