I'm tempted to sign up to online bingo, just to see if I win, but don't know if this is a good idea. I don't want to get obsessed! Also, how likely is it that you win and is it safe?

Why don't you try Gala Bingo. There are a number of free games every Thursday, winnings ranging from a fiver to £70. And the best part is that you don't have to enter any card details whatsoever (when it asks for them just close the window as you will still have completed registration) and if you win just get them to send a cheque. First time I played on there I won £70, not bad for a few hours work!
Or you could just sign up to one of the sites that offers a free few quid to try it out.