It was bad luck earlier this week.  But who knows, maybe yet another user is attacking (it isn't the previous withholders).  You can read above for why it's impossible to detect an attack unless it is sustained for long enough time to provide statistical anomalies for users.  But the bad luck spike we had lasted only a few days, and was caused by just a few very poor rounds.  The pattern does not fit an attack because we'd have a few normal length rounds, then one or two bad rounds, and then back to normal.  There weren't any significant speed fluctuations between those changes.

Eligius was able to hold 200 BTC hostage because Eligius does not pay out regularly.  BTC Guild pays out multiple times per hour.  Even if I froze the user's accounts, you'd get maybe a dozen, two dozen coins.  In return, you'd end up with some very pissed off people who already know how to weaponize their ASICs against a pool by simply reverting a patch.