As someone who deals with QA on a daily basis, if you dont have proper logging, you won't catch anything and then say "oh we can't reproduce this error".
Rito - have proper logging and a bunch more bugs will suddenly become reproducible on your own machines.
We have pretty good logging on a per plugin basis. It is harder to determine the sequence of events that led to a bug when multiple plugins have a bad interaction, hence the high value of collapsing them.