Since I am living in Greece right now, I can say 2 things:
1) The election results are not really accurate. The Golden Dawn has been around for decades, they’re nothing more than a bunch of thugs, who, as wundaytta rightly said, have used financial strife to gain social support. There is a lot of racism and nationalism, but the core thugs are no more than a couple of hundred. Those votes could just have easily gone to ND, LAOS (where they originally belonged) or AE, or even to the left wing parties. These are just desperate people thinking the Golden Dawn will help them.
2) There is however a worrying shift to the right. Understandable or not, it is real. I’m more concerned about people such as Voridis or Georgiadis joining the New Democracy party, than the rist of the Golden Dawn extremists. Because, even if most ND members (and voters) do not condone nationalist ideals, they accept such extremists in their party, and Voridis was even appointed minister for a while. Overall, Greek society as a whole is more tolerant towards extremism and less tolerant towards foreigners. They are trying to find a scapegoat, and Pakistani or Afghan immigrants seem to be an easy target.
The situation in Greece is so chaotic, that it could easily spiral out of control, even without the outside pressures. The only reason there’s no civil war yet is that people are not exactly sure who’s on the “other” side. They throw stones in the general direction of McDonald’s, any Mercedes passing by and maybe even their local Germanos phone shop, but there’s no real, easily definable “bad guy” to attack. Except perhaps Merkel, who is compared to Hitler in a dress.