I second everything Diamondback wrote
Do it, do it, do it! It is so much fun and you meet some lovely (and in my experience) like-minded people. Before you know it you will be slimmer, fitter and have a whole new family
You do not have to be fit to start, or even be able to skate, that is the beauty of it. If any league/team is worth its salt they will happily train you up and encourage you to the best of your ability.
stripeyknickers' Dh is over generalizing in regards to the 'high proportion of lesbian/bisexuals' You will find that yes, as in any other sport, that there is lesbian and bisexual teammates and a whole lot more of straight folks too. Roller Derby does NOT discriminate, we hit on anybody We allow people to be themselves, and that is why girls of all shapes, sizes, colour and sexual orientation will be more open than in other sports.
Have a look on YouTube, there are lots of great derby videos/docs on there -
My favourites being;
Eight wheel Drive
Bruitful - a roller derby documentary
Auld Reekie Roller Girls
Diamondback Oh wow you are a Blitz dame? I love you grrls! You, along with LRG has provided one of the BEST videos in a long time
Oh and watch out for This is Roller Derby film coming out next year.