I LOVE LOVE LOVE my cyclocross bike. I commute about 30 miles RT each day on it and frequently take it off road as well. In fact, just this morning I took it mountain biking up a pretty significant climb and it outclimbed 2 of our relatively equally fit party of 4 (I was the only one who was not on a mountain bike).
I was hesitant to get one because I kind of viewed them as bikes that do nothing particularly well. That has not proven to be the case. They are good at almost everything but perfect for only one thing: being a mixed use bike. It is true that in almost any situation there is a bike that could do it better, but for a single bike that does everything well, this is the TICKET.
You give up a little on the descents and fast bumpy terrain but other than that, they are wonderfully off-road-capable.
Moreover, they are suprisingly capable on-road as well. My commute group routinely gets up over 25 mph and the Major Jake has had no problems hanging at that speed (at least, I can't blame it on the bike when it does happen)
If you aren't going to be doing super high speed off road, I might recommend going with a hybrid type tire that will give you more speed on the road and still be very capable for basic off road riding. I ride the Michelin Transworld city http://www.universalcycles.com/shopp...ls.php?id=4586
and love it. I would never race that tire but for almost all of my on and off road riding, it is a wonderful blend for both worlds.
It took me a while to get used to and appreciate my Major Jake but I prefer it for just about any ride now. In fact, I almost took it on my 200 mile Seattle to Portland in one day ride. The only reason I didn't is because I knew that my buddies were speed demons and I needed every ounce of speed I could coax from my legs.
With the 35 transworld cities, the Major Jake is much more comfortable than my road bike too, and dang near as fast. It really only falls back at speeds over 25-26 mph on the flats (and that is not really a problem with the bike, more the engine; but my road bike feels a little faster). That said, I can cruise above 28 mph on the flats with the guys (with significant pain) and I have had the bike over 52 mph. So it is not slow AT ALL.
In the winter, I mount a 35 mm studded Nokian tire on the front, zip tie some fenders on, and I am good to go.
Snow: No Problem with the right tire
Mud: no problem.
Off road climbing: No problem (I run a 38/48 up front and an 11/32 on the rear w/ an ultegra short cage rear)
On road climbing: No Problem
On road high speed: No problem, but the road race bike is faster at crazy high speeds
Off road descending: No problem unless it is bumpy or super fast and steep (Brakes are a limiting factor)
On Road descending: Absolutely no problem, stable as a rock.
Gravel Roads: No problem (my first major ride on it was a 100 miles with 60 on highway and 40 on gravel)
Dirt roads: Even better: This is where the bike shines and will walk away from any other type of bike.
Deep Sand: Not so good, the skinny tires are a disadvantage
Rocky Climbs: Other than being bumpy, I can keep up with mountain bikes on non-psycho terrain.
Bottom line: I don't know anyone who owns a cyclocross bike and does not love it.