This is the best recap on the web so far of what is to come to NBG shareholders.
-12% of the new shares will be issued to the current shareholders after split and if any are left to the public. Meaning 88% belong to the HFSF(Hellenic Financial Stability Fund)
For Athens Exchange Shareholders:
-4 days of non-trading will commence on Friday May 24th 2013 and will last until Wednesday May 29th 2013 in order for the reverse split to be completed.
-Option to purchase upto 2.2 new shares for every 1 currently owned share at 0.55USD
-The reverse split will occur prior to sale of new shares
-May 27th 2013 through June 10th is the period in which you can exercise options to purchase.
For NYSE NBG(ADR) Shareholders:
-Shareholders, who are engaging themselves in the rights issue, will get warrants in case the target of 12% is met, meaning if all the shares are sold out on the Athens market.
-This would entitle you to own 7.33 shares back from HFSF per share you own.
However, warrants or rights may trade undervalue. In the case of a similar Greek bank, warrants were traded 40% under market.
User "thatwolf" in the source below says it a little differently:
" if you currently own 100 shares, they will still drop down to 10 shares. Then if you take part in the rights issue and buy an additional 10 shares, for those shares will receive 7.33 additional shares for each you own for an end total of 93 shares, so 10+10+(10 * 7.33). The first 10 are the RS shares, the second 10 being the ones bought from the rights issue, and the 10 * 7.33 are the additional shares that you receive from the HFSF once (if) the warrants are issued."