There certainly was a shift starting in the 60s when affluent urbanites began settling in VT, but the state has always been pretty egotistical and independent in a liberal-libertarian kind of way. VT voted reliably Republican from the civil war era through the Reagan years because they percieved the Democrats as too southern and too populist. They couldn't stand guys like William Jennings Bryan or Woodrow Wilson. VT also voted against FDR all four times mainly because the small rural state did not feel the effects of the depression and it's citizens saw the new deal as unconstitutional. Nowdays, the Democrats have become home to the affluent, educated WASPs while the Republican Party has gotten more populist/southern, so naturally Vermonters have flipped on the presidential level. However, the state/local Republican Party in VT is still competitive, albeit much more socially liberal than the national party. If Mit Romney wins the nomination in 2012 and runs on fiscally conservative principles, I could see Obama actually losing 5-10 percentage points in VT.
Fiscally conservative points?! Their one Representative is a self-desbribed Socialist!