Every situation is different...sometimes it really pays to chase a hot stock. I recently chased SWKS at 101, and it quickly dropped back to the low-mid 90 range. But I hold on to stocks for 6 months or longer (usually 2 yrs+), so I'm not too concerned, because I think it has great long term potential.
Many factors are involved - near the top of the list: Are you looking to hold for days/weeks/months/longer? Can you hold on if it turns around and drops 10-20% soon after you buy it? Sometimes investors bail out, and the stock sits at the lower price, for a few weeks and then resumes its upward trend. Of course, a stock could also fall back, and stay at that level for awhile. Yes, if you follow a stock's trading patterns, and you're buying a significant position, you want to be careful before buying after a recent run-up, whether it's a few points or greater.