Yeah the 8 million I mentioned is quite an outlier.  Only mentioned it because it fell in the 20-30 range I suggested.

A quick and dirty copy/paste into openoffice calc shows since the last difficulty change, Ars has averaged about 1.55 million shares per block found with the Q1 and Q3 at 0.46m and 2.25m - I was using Ars as an example of a fair pool, the actual statistics seem to show they're beating the 1/difficulty rate by quite a bit(which explains the current positive buffer).

The accuracy gets a little screwy past the precision I'm using here because there was one data point that has a share count of 0 - not sure whether to include it or not, but the effect is like a -0.6% difference (1/170) if you include it(my numbers above don't).

[edit] oh just a thought, my math professors would kill me for saying 'average' when I meant 'mean', especially since I listed Q3 and Q1 - which are usually listed along with median for box plots.  The median is 1.12mil, which shows the expected skew since numbers can't go below 0 but can occasionally get very high.