Thanks guys, exactly what i was looking for!
Given how low rates are right now during a good economy, i'm considering an ARM when we buy, or at least want to analyze the possibility. Knowing we could buy out the principal at any time if it jumped up could negate a serious upswing. Although, locking in a 30 year at 3.68% (vs. 3.39% with the ARM) wouldn't be a bad place to be either.
Who knows where we'll be in 5 years, so maybe the 0.3% spread isn't enough to warrant the gamble