I'm a diet coke addict - but I figure I don't drink coffee so I'm allowed to have something naughty...

When I've been pg I've limited my coke drinking to no more than a glass a day, and when bf I only have it just after a feed (preferably at night when DD2 is asleep!)

It's definately not good for you, so I guess you have to weigh it up... IMO it's ok to have a treat every once in a while...