Last week I went to the SQGNE talk, which was Capers Jones presenting his stats on software quality.  He's been collecting data since 1984, and he's got a lot of it.  The slides from the presentation are here: http://www.sqgne.org/presentations/2010-11/Jones-Nov-2010.pdf

There's a lot of interesting stuff in there, but 2 things in particular stuck in my mind.

First, while discussing static analysis as a defect removal tool, he said it was very effective, and generally finds different errors than testers do (which I knew), "and it's free".  Huh?  When I was last paying attention, which admittedly was quite a few years ago, the tools were expensive.  Well, sometimes it's free - apparently it is used extensively in the open source communities, so there are open source static analysis tools for the popular open source development languages.  Yay for open source!

Second, he noted "bad test cases" as a "common and troublesome" originator of software defects.  Not on what I think of as the classic list (requirements, design, coding errors, bad fixes), but oh yes, I can see that.  Test cases written by someone who doesn't understand what they're testing, that don't actually do anything to the feature they're supposed to exercise, that were originally good but didn't change when the target functionality did, that actually do expose a problem but the tester doesn't know how to look for it ...  As a tester I'm supposed to be part of the solution, and it is good to be reminded that I can also contribute to the problem.