Two quick ideas for vacuum cleaners.
<accent type="british">Ones that work properly.</accent>
Cordless Upright Vacuum
This one, I could build. I'm tempted to. Get me an off-the-shelf energy-star vacuum cleaner, a home office uninterruptible power supply, some warranty-voiding tools, a few yards of duct tape, and an afternoon, and I'll give you a vacuum that doesn't try to trip you dozens of times with its big stupid clumsy power cord while you use it. Actually I won't give it to you, I'll keep it. Even if it kind of sucks.
(...Did a quick Google search... no, not a little pretend vacuum, not a dustbuster, a real friggin' cordless vacuum. I don't care if it's heavy. I'm as strong as I am clumsy. Lose the wire.)
We don't have a roomba, but the idea is appealing. We do, however, have a spotbot, and it is worth its weight in gold because it cleans up after our runt of a cat, who can't eat anything other than one kind of prescription food, but does anyway. A spotbot which could seek out the next area of barfplops and tailsmears would be worth its weight in ... something else super-valuable.
...This one's quite a bit harder. It would need to be able to refuel itself with water and detergent (and dump out the cat-barf-tainted water) as well as deal with taller solid masses in addition to spill-type floor-level stains. Sign me up for version 2.0 of this one; working out the kinks in this design would be more gross than my current techniques.