i bought the original roomba years ago when they first came out. i usually never get an extended warranty, but decided to get a 3 year extended warranty on it just in case. apparently, that confused whoever was filling my order so they sent me 2 roombas & the extended warranty.

fast forward to almost 3 years later, a part on one of the roombas broke, so i took it back & they gave me a brand spanking new roomba discovery (self docking w/ remote, 2 virtual wall units).
the discovery is nice but i never use the remote. ever. the self docking is nice too when it can find it's way back to the base. i have noticed the discovery seems to get itself wedged into corners more frequently than the original roomba. it'll go into an area bounded by 3 objects (wall, door & chair) and get stuck bouncing off those 3 areas forever. whereas the original would figure it out. i know they changed the firmware/patterns for later roombas, but it seems to have made it worse.
the faster charger is a must, especially if you only have 1 roomba. the slow charger would take 12-15 hours to recharge my dead roomba. the fast one on the discovery takes just a few (2-3 or so). it makes a big difference between roomba'ing the whole house in a day or doing a different room every day of the week.
it works great on hardwood floors & well on our low pile carpet. unfortunately, we have a long haired dog and the roller bar mechanism always needs to be removed & de-furred after the roomba's done for the day.
overall, we're pretty happy with them and the kids love watching them run all over the place.