Yes, me too. In fact I have a triple on my bike (not tri-specific). When the only thing that's stopping me winning is that extra 100g then I'll think about changing it, but I think that day will be a long time coming....

Round here plenty of beginners use mountain bikes, with loads of low gears for triathlons - if it's your first and it's a hilly sprint, then why not (DH used his city bike, complete with luggage rack and mud-guards for his first tri).