Habbo is like Second Life with Lego people.
Create and dress an avatar, then walk around and chat with folks. Uh, that is if you have Shockwave installed, which doesn't run on Mac OS X or Linux. (Parallels running Windows XP with IE 6 works!)
Visit other people's rooms or create a room of your own for free. Though to decorate your room, you must spend Habbo Coins. Things like chairs and rugs are around a buck each ... and they have a many ways to collect your payment: credit cards, 976 numbers, prepaid cards, premium-fee SMS ... more options than a skuzzy porn site!
Overall a great idea, but the up-sell is sleazy. (Particularly when 90% of their users are 13-18 years old.) At least in real life you can scrounge up cinder-block shelving and cable-spool coffee tables ...