Actually, the Lisbon treaty was the first EU treaty to give countries an easy way out of the EU, should they ever so desire.

But no goverment in power seems like they would be willing to do that, and without a willing goverment you won't pull out, and there aren't scheduled referendums asking if they want to stay in the eu.... for example in the uk in current political climate your only option would be voting UKIP, who will never win an election, so you could never get out once your in basically... barring as i said major circumstance change, of course if a goverment was willing im sure it would be easy, but with major political parties all being pro eu (in uk) you wouldn't have a choice...