A cyclocross bike will also be a lot lighter than a hybrid, possibly by a few to several pounds. That will help if you do any hill climbing. Velogirl gave some great examples of why cyclocross bikes are fun. I've taken mine on mtb trails, and while there aren't any nice shocks to absorb the bumps, the bike is so limber that it is a whole different beast on the trail. For commuting, I'd look at the terrain you'll be doing. I can climb short distances at 15% on 38-26 on my 'cross, but I can't do any of the steeper hills in my city with it (yet anyhow). I like the wider tires when commuting too. I haven't put any road tires on there yet, but I have a plan to at some point.

If you find that you're going to do a lot of trails and commuting with the bike (and not races) you might want to look into a model with disc brakes. My only complaint about my cross is the brakes. I don't feel too safe descending in the city..but I have a lot of hills to contend with and you might not.