I just bought a Roomba 651 and tried it out for the first time yesterday. It took about 90 minutes to clean my 65 square meter 700 sq. ft. apartment. The floors were already pretty clean and it still nearly filled its receptacle with dust, so I am impressed with the way it worked. But QUIET IT IS NOT It may be a bit quieter than a regular vacuum, but still very noisy. You won't be watching a movie on TV while this thing is working. It's also not a replacement for your vacuum, but rather something for daily 'touching up' between heavy cleanings. The one problem the Roomba had where it needed my assistance was the bath mat. It pushed the mat into a bundle and couldn't maneuver around it. I took the mat away and it happily continued to clean the apartment without further need of assistance. Was it worth the 1, 500nis 385 USD I paid for it? Yes. I think so. It's worth noting that, from what I understand, the difference between the 651 and the 631 is that the 651 can be programmed to clean at specific timesdays where the 631 has to be started manually. I haven't used the programming feature yet, since I can just start it before heading out for work, but I may use it later.
We have Roomba 530 for 4 years now and it's still going strong. I still have the original NiMH 3000mAh battery inside. It lost some capacity, but it's still enough for us. Since we have the Roomba, I've never had to vacuum clean the apartment by hand. In fact, it pulls my wife's hair from the carpet better than the regular vacuum cleaner ever had.