Market timers are more bullish today than they were at the highs in May, says MarketWatch's Mark Hulbert. From a contrarian standpoint, this could mean trouble. The average stock market exposure recommended by short-term timers currently stands at 50%, compared to May's correction where is stood at just 42%. If these bulls get stubborn and dig in their heels, it's going be one heckuva run to the downside when they finally break. One caveat however: Watch the volume, if the bullish timers run for the exits too quickly, the any pullback will be modest at best.