Sorry, but the company I just left used Mantis. After coming from Fogbugz(a GREAT bug tracking system), Mantis was extremely inefficient to use. I cannot recommend it to anyone.

I would like to ask a) what version of MantisBT was your company using, and b) what did you find about it that you didn't like?

MantisBT has made a lot of strides in both features and usability recently, both in the current 1.1.x releases and especially with the upcoming 1.2.x plugin system. It's gained a lot of potential that other free/open issue trackers lack.

But I'm most likely biased, and I would like to hear others' opinions of the matter...

You have a good point. I'm honestly not sure what version it was. The company always used old software(5 year old Vignette cms). That probably has unfairly influenced my views of Mantis. I still recommend Fogbugz but try Mantis too