How the Bitcoin community will handle attacks on a Client's code?
FYI since BTC mining became so prohibitively expensive due to use of ASICs 1 51% attack could be pulled off at any time by BTC Guild. Their listed % is just under 50% at ~48% but I find it hard to believe they aren't sitting on >51% mining power. See the problem is every client is meant to be able to mine making large conglomerates like BTC Guild impossible.
This could very well be the end of BTC since you've got no change at all of mining BTC using anything but an ASIC pool.