I bought the 
Hoover SteamVac although I was more interested in the 
Bissell ProHeat.  Every store I went to had them on display but were out of stock and only had the ProHeat 2 which was nearly $100 more.
If your carpets are in good or like-new condition, this thing is great.  I've used professional carpet extractors and this is the closest thing I've found to it.  I tried those bulky Rug Doctors and found them to be mostly useless.  They were being rented for $24 a day so I figured buying one would be cheaper in the long run.
It didn't do as good a job on the heavily-trafficked areas but after six years, it's time for some new carpet anyway.