I have found it nice in general to use Mantis.  One improvement is the
speed.  I frequently avoided using BFAV because I would have to wait for
many minutes while it downloads the email database.  Another is that I
like and understand filtering that Mantis has built into it.

I certainly liked having a Squeak interface, though.  It was especially
nice being able to browse code proposals without having to save them to
a file and then reload them in Mantis.

FWIW.  I expect that using an off-the-shelf bug tracker is going to be
the fastest way to getting a pretty good bug tracker, and that a little
Squeak hacking can turn any pretty good web-based tracker into an
excellent one.  If someone wants to really work on a Squeak-based
tracker, including getting the performance improved, then that is great,
but given that that doesn't seem to be happening....  If someone is into
bug tracking technology, but has limited time, then a great way to get a
lot of results from a little bit of effort would be to make a BFAV-like
GUI that talks to a web-based bug tracker.

-Lex