Using a bit of simple java to read slush's api - I am now storing all results going forward - here's what I have for the last 96 blocks...
Pretty consistent I find... Note the result for 237575 - I don't mind admitting this was way more than expected and others complained about this block.
block=start_time,duration,reward,hashes,luck,difficulty,confirmations
238076=2013-05-26 22:26:09,0:42:39,0.00722143,10284,0.93,12153411,
238072=2013-05-26 21:43:30,0:35:45,0.00809340,10804,1.03,12153411,
238067=2013-05-26 21:07:45,2:23:55,0.00704795,10595,1.08,12153411,
238052=2013-05-26 18:43:50,0:20:55,0.00641399,10583,0.91,12153411,
238048=2013-05-26 18:22:55,2:14:21,0.00717486,10482,0.94,12153411,
238033=2013-05-26 16:08:34,1:11:51,0.00704562,11814,0.88,12153411,
238029=2013-05-26 14:56:43,2:04:08,0.00745546,10597,0.90,12153411,
238017=2013-05-26 12:52:35,1:14:40,0.00619396,10766,0.88,12153411,
238003=2013-05-26 11:37:55,1:21:22,0.00620576,10772,0.89,12153411,
237996=2013-05-26 10:16:33,1:24:44,0.00733699,10410,0.88,12153411,
237983=2013-05-26 08:51:49,2:13:47,0.00743041,9189,0.90,12153411,
237971=2013-05-26 06:38:02,3:11:30,0.00717705,10238,1.02,12153411,
237951=2013-05-26 03:26:32,2:54:45,0.00710204,10340,1.41,12153411,
237930=2013-05-26 00:31:47,0:33:15,0.00847152,10582,1.08,12153411,
237928=2013-05-25 23:58:32,0:25:35,0.00719589,10502,1.01,12153411,
237921=2013-05-25 23:32:57,1:00:46,0.00725148,10399,0.99,12153411,
237915=2013-05-25 22:32:11,0:26:24,0.00692039,10658,1.01,12153411,
237911=2013-05-25 22:05:47,0:39:06,0.00715212,10543,0.94,12153411,
237904=2013-05-25 21:26:41,0:01:08,0.00719272,10639,0.86,12153411,
237903=2013-05-25 21:25:33,0:28:52,0.00755953,10650,0.86,12153411,
237901=2013-05-25 20:56:41,4:16:32,0.00771986,10560,0.95,12153411,
237878=2013-05-25 16:40:09,2:42:32,0.00676582,10401,0.98,11187257,
237854=2013-05-25 13:57:37,1:33:22,0.00725034,10533,0.99,11187257,
237840=2013-05-25 12:24:15,1:04:10,0.00730492,10564,1.09,11187257,
237833=2013-05-25 11:20:05,0:01:38,0.00736490,10489,1.14,11187257,
237832=2013-05-25 11:18:27,3:04:34,0.00771931,10504,1.14,11187257,
237818=2013-05-25 08:13:53,0:08:27,0.00794650,9750,1.14,11187257,
237817=2013-05-25 08:05:26,1:39:50,0.00806913,9621,1.14,11187257,
237807=2013-05-25 06:25:36,0:29:47,0.00783007,10626,1.13,11187257,
237802=2013-05-25 05:55:49,0:32:47,0.00780047,10622,0.93,11187257,
237799=2013-05-25 05:23:02,0:18:18,0.00785517,10668,0.90,11187257,
237796=2013-05-25 05:04:44,0:44:33,0.00764717,10544,0.87,11187257,
237791=2013-05-25 04:20:11,0:13:41,0.00746889,10642,0.81,11187257,
237789=2013-05-25 04:06:30,0:39:30,0.00735985,10590,0.81,11187257,
237787=2013-05-25 03:27:00,0:05:17,0.00755139,10640,0.77,11187257,
237785=2013-05-25 03:21:43,0:15:41,0.00727747,10611,0.78,11187257,
237784=2013-05-25 03:06:02,1:57:45,0.01005058,10515,0.73,11187257,
237770=2013-05-25 01:08:17,7:13:34,0.00784526,10564,0.96,11187257,
237719=2013-05-24 17:54:43,0:02:26,0.00866961,10413,1.21,11187257,
237718=2013-05-24 17:52:17,0:04:50,0.00671417,10399,1.21,11187257,
237717=2013-05-24 17:47:27,4:38:12,0.00875716,10376,1.08,11187257,
237692=2013-05-24 13:09:15,0:00:47,0.00659933,10251,1.11,11187257,
237691=2013-05-24 13:08:28,0:21:19,0.00809546,10259,1.11,11187257,
237687=2013-05-24 12:47:09,0:49:59,0.00851697,10232,1.10,11187257,
237682=2013-05-24 11:57:10,0:17:29,0.00787294,10179,1.08,11187257,
237679=2013-05-24 11:39:41,1:46:36,0.00817001,10088,1.09,11187257,
237666=2013-05-24 09:53:05,1:41:22,0.00733902,10022,1.15,11187257,
237652=2013-05-24 08:11:43,0:18:19,0.00839849,9551,1.15,11187257,
237648=2013-05-24 07:53:24,0:05:31,0.00743627,9637,1.03,11187257,
237647=2013-05-24 07:47:53,1:48:51,0.00808714,9718,1.03,11187257,
237634=2013-05-24 05:59:02,5:59:04,0.00805881,9854,1.37,11187257,
237593=2013-05-23 23:59:58,2:17:42,0.00833270,9817,1.45,11187257,
237575=2013-05-23 21:34:50,0:07:57,0.02476670,10034,1.38,11187257,
237574=2013-05-23 21:42:16,0:07:26,0.00742560,9665,1.38,11187257,
237573=2013-05-23 21:26:53,0:06:46,0.00705477,9984,1.38,11187257,
237571=2013-05-23 21:20:07,0:28:39,0.00750324,9964,1.38,11187257,
237567=2013-05-23 20:51:28,2:06:53,0.00531363,9869,1.32,11187257,
237559=2013-05-23 18:44:35,1:40:46,0.00840785,9782,1.36,11187257,
237546=2013-05-23 17:03:49,0:12:37,0.00849736,10025,1.22,11187257,
237543=2013-05-23 16:51:12,0:18:22,0.00750947,10025,1.17,11187257,
237541=2013-05-23 16:32:50,0:09:48,0.00772226,9895,1.09,11187257,
237540=2013-05-23 16:23:02,0:37:17,0.00812397,9867,1.09,11187257,
237534=2013-05-23 15:45:45,3:00:18,0.00925976,9716,1.18,11187257,
237517=2013-05-23 12:45:27,0:15:24,0.00806292,9663,1.23,11187257,
237515=2013-05-23 12:30:03,0:41:01,0.00737965,9567,1.18,11187257,
237506=2013-05-23 11:49:02,1:40:20,0.00873779,9401,1.20,11187257,
237495=2013-05-23 10:08:42,0:37:26,0.00868290,9416,1.26,11187257,
237493=2013-05-23 09:31:16,2:23:19,0.00842615,9206,1.35,11187257,
237468=2013-05-23 07:07:57,0:26:47,0.00878185,9515,1.18,11187257,
237463=2013-05-23 06:41:10,0:58:02,0.00763858,9457,1.17,11187257,
237455=2013-05-23 05:43:08,0:12:24,0.00729014,9475,1.06,11187257,
237454=2013-05-23 05:30:44,0:37:06,0.00768914,9348,1.06,11187257,
237447=2013-05-23 04:53:38,3:17:55,0.00802322,8912,1.17,11187257,
237430=2013-05-23 01:35:43,0:04:00,0.00742885,9404,1.06,11187257,
237429=2013-05-23 01:31:43,0:06:52,0.00844826,9387,1.06,11187257,
237427=2013-05-23 01:24:51,0:13:37,0.00872385,9399,1.02,11187257,
237426=2013-05-23 01:11:14,0:25:39,0.00872593,9450,1.00,11187257,
237423=2013-05-23 00:45:35,0:07:22,0.00838761,9474,1.03,11187257,
237422=2013-05-23 00:38:13,4:04:19,0.00840443,9444,1.03,11187257,
237404=2013-05-22 20:33:54,2:16:21,0.00872369,9649,1.03,11187257,
237396=2013-05-22 18:17:33,3:04:10,0.00841272,9377,1.10,11187257,
237373=2013-05-22 15:13:23,0:16:44,0.00714505,9546,1.06,11187257,
237371=2013-05-22 14:56:39,1:26:03,0.00824117,9459,1.07,11187257,
237358=2013-05-22 13:30:36,0:18:05,0.00772997,9566,0.90,11187257,
237355=2013-05-22 13:12:31,1:26:50,0.01115425,9484,0.90,11187257,
237343=2013-05-22 11:45:41,0:09:11,0.00820818,9427,0.90,11187257,
237340=2013-05-22 11:36:30,1:28:06,0.00911549,9351,0.84,11187257,
237331=2013-05-22 10:08:24,0:05:28,0.00823078,9468,0.74,11187257,
237330=2013-05-22 10:02:56,0:45:39,0.00851554,9419,0.74,11187257,
237322=2013-05-22 09:17:17,3:48:29,0.00851632,9354,0.80,11187257,
237296=2013-05-22 05:28:48,1:38:40,0.00833779,9147,0.77,11187257,
237286=2013-05-22 03:50:08,2:18:08,0.02264307,9074,0.77,11187257,
237274=2013-05-22 01:32:00,0:22:36,0.00856823,9147,0.66,11187257,
237270=2013-05-22 01:09:24,0:44:11,0.00845058,9200,0.66,11187257,
237265=2013-05-22 00:25:13,2:00:35,0.00891731,9017,0.65,11187257,
[EDIT] my post is longer than yours