Bearing down

[steeeve66]

Just had a rear wheel bearing fail on me - fortunately just a couple of miles from home so I was able to 'limp' back. I've seen it happen to others but only on much higher mileage machines (40k+), my 04 gen 1 has only done 20k, does that seem low for a wheel bearing failure? What sort of mileage should you get from bearings? And should I be replacing the front bearings as a precaution?
S