Are 32mm tires ideal for a fast commuter bike? I am considering a faster bike to replace my XC for commuting. I am thinking hybrid/cross/road bike with wider tires. My question is whether 28mm tires are enough or if I should go with 32mm like Trek touts for their CrossRip. I won't be riding gravel roads or other heavier terrain too much, but I will need to jump to/from curbs from time to time.

Where I live I often need to ride over cobblestones and tram tracks, like this, so safety is very important:
I commute on two bicycles: 
— a road bike, with 25mm tire up front and a 28mm back.
— a custom commuter bike, with 32mm up front, 35mm back.

I'd recommend you go with the 32mm tires.

The 28mm tires I've used are good for commuting (I think the 25mm I have is too small — I have to give it too much attention when crossing curb lines and such).

That said, 32mm tires offer a lot more protection in urban environments. I ride suburban roads (25mm is fine for those) into an urban environment, and then I go into a college campus.

It is on campus where the 25mm tires get dicey. There are many different surfaces on campus, and each change creates an edge — It is those edges that will get you, either trip you up or cause a pinch flat.

A 28mm tire does OK, but a 32mm tire handles these conditions much better.

Some 32mm tires are heavy, some are lighter weight. For what you hope to do — go fast — search around for lighter weight tires (Panaracer might be a good place to start).

Enjoy the fatties!