I cam to this forum looking for help with my Robophilo, but smiled when I saw this forum, as my 2nd robotics project is a lawnmower. Right now it's just an R/C lawnmower, no intelligence yet, but it's still really cool. I bought an arduino to be the brake controller, and it will also eventually be a remote kill switch.
I've got a few videos on my youtube page (same name as here) if you wnat to see it in the various stages of completion.
Also, I am interested in manufacturing these and aside from making it, I think the biggest point of interest/concern is the possible liability. The USA of today is sue-happy; would I need a corporation with tons of liability insurance to sell these?