Did you sign a lease holding you responsible for the full month's rent? If so, you are SOL as you are legally responsible for covering for your roomate when he flakes out... It sounds like your landlord is being cool, but if they decide not to, they could fuck up your credit...
My current landlord tried to pull that kind of lease on me, but I refused to sign anything obligating me for more than my 1/3 (renting a house).
As for the "take him to court" -- I don't think most of you guys have dealt with scumbags like this in court. Here's how it works: you go to court, the judge agrees with you and finds in your favor. Roomate legally owes you back rent -- woohoo. Now try to collect the money. Oh, and by the way, you just spent a bunch of time and some money taking this to court -- so now you're out the rent + your time & court fees!
On Judge Judy, the TV show actually pays any damages (which is why people agree to air their dirty laundry on the show). In real life, you've got a judgement in your favor and no way of collecting...