According to current studies you'd be at an increased risk of skin cancer. Then again, people who sunbed are probably the same people who don't put on enough suncream when they're tanning on holiday, so that might make up some of the cases.
Either way, I wouldn't do it myself. How about a spray tan?
Only using them once a week for 3mins isn't going to do anything unfortunately. I was quite pale and had to go on for two weeks, starting at 4mins and working my way up to 8mins, before I saw any difference. You've got to keep going for a while after that too in order to top up and keep your tan.
I went on them almost everyday for 3 months and it's the stupidest thing I've ever done. I started getting all these raised lumps on my stomach and so went to my doctor. I got a free skin consultation under a UV lamp and I couldn't believe the amount of irreversible damage I'd done to myself in such a small amount of time. I've found a brilliant fake tan called St Moriz, which is cheap and absolutely amazing, definitely the best one I've used. Give that a try instead, once you begin tanning on sunbeds it's very, very hard to stop and I wish someone had prevented me from even starting.