In response to rds's review, he probably hasn't looked at Bugzilla in a few years. It did indeed used to be exactly like he says, but it's changed a lot in the last few years. Installation is only as hard as your OS's Perl installation makes it (and that's getting better all the time with most distros already having most of the prerequisites now). It's pretty speedy if you run it under mod_perl. The ability to customize it is one of the big selling points these days.
Given the choice between current contenders (bugzilla, rt, trac, mantis) I'd still choose Bugzilla anyday.
It is incredibly customisable and far easier to get started with than either trac or mantis.
The documentation and support is superb - I was able to brand, add extra reports, integrate a blog and cvsweb, and provide custom front pages and searching in a matter of hours, and that was back in 2002, 6 years ago - it's improved a fair ammount since then, and with it's use of TT, Classes and CPAN libraries is probably the most customisable and extensible bugtracking system available.
Having used commercial bugtracking systems I can safely say then don't even come close.
After looking around for a long time and using one bug tracking system after the next only to be disappointed by one thing or another I eventually settled on Mantis but I was never thrilled with it. Mantis is entirely designed for programmers to use, not end-users.
I had avoided Bugzilla for a long time (and I'm embarassed to say this) because of its name. I really hate the '-zilla' suite of names but once I saw how a live system worked with SDL's installation I immediatly knew that this was the bugtracking system I wanted.
It was a little tough getting it installed properly on a web host that I wasn't physically sitting at but once I learned how to log in to a terminal session remotely the installation was actually pretty straight-forward and went pretty smooth.
There are a few things that I would change about Bugzilla's interface but the reality is they're really minor points (and more than likely I can customize it... just need to read the docs). Ultimately the system is much better suited for knowledgable non-programmer end-users (you know, the ones you actually *want* sending you bug reports) and has a superior administrative back-end.
I've only been using Bugzilla for a short time but, quite frankly, I'm thrilled I installed it.
If you ever used free/libre open source software "actively", Bugzilla certainly feels like an old friend. Bugzilla makes it easy to track and find whatever amount of issues and it's highly flexible in configuring what levels of complexity are exposed to users, as well as in the levels of involvement expected from users (starting from simple things such as what email notifications to receive).
Hard to install and maintain, pretty slow, and almost impossible to customize. Why would you want such an issue tracker when there is Mantis, Trac, Scarab, TrackIt, jtrac. (if you want a commercial solution, I would recommand Jira)