I was reading through the historical Bitcoin incident list. Specifically, the overflow bug incident -http://bitcointalk.org/index.php?topic=822.0
The block chain had to be forked, with the new chain overtaking the "bad" 8 hours later..
Forum members were on to this quick.. and people patched their clients fairly quickly. I believe this all happened prior to GPU mining taking off.
What might happen if a similar software bug incident occurred in future where there were many variants of CPU/GPU miners? Some miners may not visit the forums so frequently.
I do see there is a continuing trend towards pooled mining, with 40%+ of network capacity currently in the hands of 2 pools/people. I suspect these 2 contacts could potentially quickly help(?) any future incidents. A lot of centralized power right there!
The more pools the better I think. The more coders the better! Clearly the handful of developer/s actively working on Bitcoin are talented, but more eyes reviewing code can only be a good thing.
EDIT - I've just realized the miners communicate with the Bitcoin client itself via server option. So, I supposed I've answered my own questions. Provided that pool operators were on the ball, a future exploit should be caught quickly.