Iceland never defaulted. They just (prudently) refused to guarantee certain debt of their failed banks (something that Ireland should have studied much more closely before doing the opposite).

They found other creative solutions to maintain a banking sector sufficient to service their (relatively small) domestic economy; solution which may or may not work in bigger states.

If investors did learn something from that is "do not lend money to loosely regulated Icelandic banks" - which do not exist any more anyway.

They also might learn "trust the instincts of Icelandic politicians" - which actually could improve their bonds' reputation.