probably depends on the boat and just how you do it. I have dipped the boom many times on many boats. It will just push the main back and as long as you come up again no harm done. If it is the result of a major, continuous gust, it can pin you down as you cannot ease the boom. Since you are rolled way over towards the boom, and the rig is well offset to that side, you are more likely to broach to weather ('round up') than to leeward ('round down') - the wind pressure on the rig is pivoting the boat that way. When you roll back up, if the water has made the boom come back a ways, it will snap forward with a bang!

If you have a preventer rigged to the rail from midboom, there is the possibility of breaking the boom. I have had a pretty good rooster tail coming off the end of the boom at times, lots of pressure on it in those situations. One thing some people do (or at least talk about doing) is using a "tripping reef", that is, tying in the first reefing point at the clew and leaving full hoist at the tack, topping the boom up at the end. That raises the boom at an angle and delays dragging. You can even have a special reef point set in the leach for just such use, a few feet up.