Here comes a short novel...
I've had a Roomba Discovery for 3 years.
I have hardwood floors and a throw rug in the living room. The standard upright vacuum cleaners would just spin dirt/dust into the air before the vacuum head ever reached the debris. (It had an agitator on the front, ideal for rugs...terrible for hardwood no matter how high you had it above the floor)
At the time I worked part time for Sears. As these were new, they were offered to us with a substancial discount.
The Pros:
Push button, walk away.
Not loud. About as loud as a hair dryer on low.
Gets under beds, couches, etc...hard to reach stuff.
Excellent at nabbing pet hair/dander
Excellent support. Mine had a sensor issue where it would spin in circles. 2 days later, a USB thumb drive arrived. Plug into port, power up Roomba and watch it load new version. Problem solved. Mail thumb drive back.
The Cons:
High amount of cleaning required to the actual unit. If you don't mind investing about an hour a month to clean the brushes and stuff, its fine. The newer models seem to include special tools to make this easier.
Filters and accesories are limited...so buy em online or at Sears. You seldom see them elsewhere.
Batteries dont seem to last long as they get older. Mine's red (low) after 30 mins.
As they are so low to the ground, if you have a moderate amount of pet hair/debris on the floor, it just pushes it along....unable to stuff it underneath itself.
They have excellent vacuum power. Left unattended, they will suck up a floor mat and drag it around.
Don't bother watching the thing at work. You'll watch it just miss debris for several minutes. It has an algorithm it follows to eventually hit every part of the room 3 times.
Summary:
These are pretty cool devices. If I had to give it a 5 star rating, it would be a solid 4. The cool factor is up there but having to see if its really picked up everything is a draw back. NOTE!! Newer models have improved on these issues...larger waste bins and more. And the price has come down substancially. I still have the power broom (dirt devil) I use in conjunction with it for bigger jobs.
The Scooba is a floor washing variant that looks neat...but for that amount of money, Id rather get a floor scrubber.