It wasn't proprietary software, but I used to work with a sustaining engineer who ran Firefox in a gdb session. He was a "tab hoarder" and this was before the days it would save your session; when it reset he complained that he'd lose days of context. I watched him hand-repair a SIGSEGV from a null pointer dereference. As he was doing so he explained he'd reported this particular bug a few weeks ago but "Mozilla's triage was taking a while." A few keystrokes later he'd backed up a couple of frames, set a condition variable to avoid the bad code, and continued the process without interruption. Hugely impressive.