To heck with Roombas.
I want a LAWNBA.
A nice little self-operating lawn mower. You program your yard’s shape somehow, or maybe plant electronic stakes at each corner, and then turn it loose. It happily (and quietely) munches away at your lawn, plugging itself in periodically.
Set it and forget it, as that Ronco guy says.
Heck, make the thing solar-powered. I’d be ashamed to say how much I would be willing to pay for one of these.
They are out there:
http://www.ebay.com/itm/RL2000-Base-Station-Robomow-/320721940503#vi-content
Wooo! Why hadn’t I come across this before? 
If it makes you feel any better, I found out about robotic mowers a few years back exactly the same way you just did: by asking, here on the Dope, why the heck someone hadn’t invented one yet.
This one will set you back only about $1200, fwiw.
Haven’t bought one because they all seem to cut the grass a bit on the short side for my tastes. And Consumer Reports hasn’t been particularly impressed by any of them yet.
Ahh, you guys are all for spending too much money.
Red Green made on for cheap some time ago.
(Ignore what happens to the lawn gnomes.)
In the spirit of the OP:
TELEPORTERS! Come on guys, get on this teleporter technology! And invent some Futurama-y traveling tubes while you’re at it.
They have them all over Jamaica and other countries. They’re called goats.
Crap! I swear I just came up with this last week! My coworkers and I were joking about sitting out on the deck watching it miss spots over and over and over again.
And they fertilize for you, too!
~VOW
I wish I could have a cell phone with two phone lines. That is, one number for friends and co-workers and my mom and such and another for business-related calls. They’d be totally separate lines- different numbers, different ringtones, different voicemail messages, and so forth, but on the same phone.