We're all using our free time in a way which makes sense and fun. Finding bugs, correcting them and even rewriting code just because once in the past we took some shortcuts and now we're seeing the unwanted effects is not fun.

Well... actually... I've been doing exactly that for three years on the XCSoar project now and let me tell you that this can be fun too. For me it was a learning experience that ultimately got me my current job and a few other things before that.

and @Paolo: why do you have unit tests if you don't even trust them?