I have had a cat genie for nearly two years now and I absolutely love it, but I will say that it's not for everyone.
The pros are that it takes care of everything by itself... I can go for weeks without even having to think about cat litter or the litterbox. Every couple of weeks I need to add a bit more of their litter to the bowl and every two or three months I need to change the solution cartridge. When I change the cartridge I need also need to clean one of the electric sensors, but that's a 5 minute job and not messy. The best part is that I *never* need to change cat litter or deal with dirty or used cat litter at all... it has been nearly two years since I've had to touch used cat litter. Even with the littermaid and the litter robot you still need to dispose of the used litter, but this just flushes everything down the drain.
The cons are that it is rather expensive... and as a PP said, you do need to use their litter and their solution. I originally got it hoping that it would cut down on my cat litter cost, but I've found that because their stuff is reasonably expensive it really doesn't save money there. However, if you buy the products in bulk (usually I buy from
Amazon when they're having a sale) you won't spend much more than you would on litter anyway.
Also, when it works it's great, but when it has a problem it can be really bad. They've made a lot of improvements on the CatGenie in the two years that I've owned it and it has probably been 8 or 9 months since I've had any sort of a clog in the drain, but it is possible to get a clog occasionally, and when that happens you can wind up with a catgenie that is full of water and... um... cat waste. It can be a bit of a job (make sure you have a pair of rubber gloves) to clean that up if it happens, but like I said, it is very rare for something like that to happen now.
It works by scooping to poop, then washing the litter, then using heated air (almost like a hairdrier) to dry the litter. Once in a while the scooping cycle will miss something and it will get cooked during the drying cycle. Cooked cat poop is not a very pleasent smell. Luckily this too is a reasonably rare occurance for me, but it seems like some people have more problems with this than others. If your cat's poop tends to be soft it seems that it's more likely to happen.
It does require a connection to your plumbing line (in a bathroom or a laundry room), so it takes a bit of work to first install, but it's really not too hard and once it's installed then you're done. It also tends to be a bit loud when it runs, so if possible you might want to avoid installing it near a bedroom. It is possible to schedule it so it doesn't run at night, however.
Finally, I suspect that the reason you're seeing a lot of them on craigslist and such now is that they recently introduced a new model (called the catgenie120). This new model lasts longer between cartridge refills (you get 120 cycles per cartridge instead of 60 on the old model), but the big advantage is that you can set the new model to automatically run 10 minutes after a cat uses it. The old model (what is likely on the craigslist postings) can only be run manually or at specific times during the day. Having used both models I can say that it is *definitely* much better to get the new automatic model and it's definitely worth spending a bit more on.
HTH and feel free to PM me if you want any more info,
Brett