Longest rounds of which I have a record:
time height difficulty d1Shares Pool Percentage of difficulty
1367715657 234559 10076292.9 118804825 Ozcoin 1179.0529
1388874416 278626 1418481395.3 14035657031 GHash.IO 989.4847
1350495993 203721 3072321.7 30298811 DeepBit 986.1861
1312067691 138856 1690895.8 16180592 DeepBit 956.9243
1383824482 268397 510929738.0 4794448042 Eligius 938.3772
Shortest rounds of which I have a record:
time height difficulty d1Shares Pool Percentage of difficulty
1389123527 279163 1.418481e+09 718.000 BitMinter 5.061751e-05
1334195271 175309 1.626553e+06 26.000 DeepBit 1.598472e-03
1316882164 146724 1.755425e+06 41.000 DeepBit 2.335616e-03
1384619731 269959 5.109297e+08 28153.106 EclipseMC 5.510172e-03
1332828390 173074 1.498294e+06 96.000 Itzod 6.407286e-03
(Note: all data is that which was reported by the pool on its website or API.)
Yep, that's the one I'm talking about on Ozcoin. 11.79 times difficulty. A lot of users ran away from Ozcoin when that happened because of the hack and another nasty block a day earlier. People will do irrational things out of fear sometimes (as if you can escape bad luck).
if Deepbit had an 18x block, that would be pretty darn painful. It's before my time (2011).