Given decentralized distribution is a crucial factor for a POS system to be secure:
How is it made sure that bitshares is distributed enough (no too big players or groups of players have too much stake) and that the user base is wide enough?
What could be measures to (further) improve on this?
And most important: How can the distribution be measured?
Also flat distribution and a wide user base are quality attributes to any DAC / crypto currency apart from security reasons because it will be perceived as more fair.
Fairness is defined by equal opportunity and in the case of BTS we have 50% distributed "fairly" by CPU mining. With AGS everyone has equal opportunity whether they have $1 per day to contribute or more. Large investors are forced to dollar cost average their investment which gives smaller investors equal opportunity to get a stake.
I cannot think of a more fair distribution model. Especially as the distribution occurred long before the product was on the market and thus anyone with some knowledge could get in.
As far as the largest share holders... I know one guy has been contributing an average of 10 BTC per day to the AGS address, which means he has about 20% of the AGS right now or 10% of the BitShares.
The PTS Angel Address has about 10% of the PTS or 5% of the BitShares.
As far as I know these are the two largest positions.