Some people sell a little at a time as the price goes up. Others sell enough to recoup their initial investment and then keep the remaining "free" shares longer term. Others who are up for more risk might choose to hold on to all their shares for awhile. If this bank and Greece's economy improve, the price could go up significantly. Or if there is more bad news and/or more dilution of common shares, the price could go back down. I've held onto risky shares and made money, and I've also held on and lost money. I've made a quick buck and was glad I sold, I've also sold too soon and missed out on bigger gains. With regard to NBGGY, I plan to hold my shares long term as I think there's a decent chance it will go way back up.
Congrats on getting in cheap and good luck with whatever you decide to do.