Some people have already hit the nail on the head. The "CX boom" hit Stockholm, Sweden years and
years ago simply because you could get a decent all-rounder / all-weather reliable bike to cope with
tarmac, any badly maintained bike paths, forest path short-cuts, any unsurfaced roads, and the constant deviations through the ever increasing construction sites. Basically, they are perfect for commuting from
far into the city without any hassle.
They truely are the kind of bike to just put your leg over it, and just ride. Obviously there are limits,
but you would be very surprised just how capable they are for light XC type stuff. As somebody said,
a bit like the early days of full rigid MTB to go anywhere, and just lift or carry your bike if it gets
too gnarly or there are obsticles (obviously what the CX pros can do is damn impressive).
What you will miss though coming from the MTB world is traction off-road. Typically a 35c will
spin easy if you climb off the saddle, so you may need to change your style and sit down with
lower gears. Cornering is always a little more thrilling, and more about slowing down and keeping
the gas on rather than jamming on the brakes at the last second. IMHO disk brakes on a CX is
overkill unless you love riding in mud all the time. Personally I'm using semi-slicks, but tend only
to go out on the CX for long rides in dry conditions. Sometimes I've got carried away off-road, which
usually results in truing up the wheels so I do recommend something beefy. If it's muddy, then
I opt for the more capable MTB with proper mud tyres.
If you are from a road background, you will miss the top-end speed and need to be content with
a lower average speed but you will gain comfort and have fewer punctures.