Really? I use and love BitBucket, but the last 2 places I worked at used JIRA and it was the worst project management tool I've ever used. I'm sure someone will say they didn't configure it right or educate the devs or something. Seriously though, it was pushed down from upper management in both cases and it was a terrible experience. Then they thought Greenhopper would fix it, ha. (This was about 4+ years ago)
Edit - According to the comments below it sounds like my experience was a result of trying to do too much with it. I just might play around with a bit just for some bug tracking with some of my BitBucket projects.