This article cites a study that found programmers don't use 'program comprehension' tools:

>>Our results reveal a gap between research and practice, as we did not observe any use of comprehension tools and developers seem to be unaware of them

Oh I beg to differ. I deal with a gnarly legacy code base every day, tail -f and grep are my 'program comprehension' tools of choice nowadays. Ie exercise the UI, watch the log for something I can grep for, and read.