my centre drive shaft bearing started growling and then catastrophically failed at about 375,000 kms.
if it's not making any noise , i'd suggest you can crawl under the car, peel back the rubber doughnut flex disk a bit, pop the dust cover off the bearing assembly and re-grease and inspect the bearing, without even taking the driveshaft apart. (you'd just have to lower the support brace for the centre bearing) pretty easy about 30 -45 minute job... and probably worth doing, if your riding on a dry bearing.

i'm up in the salt belt of canada/quebec so 375,000 till failure is probably a pretty good life.

the rear wheel bearings i've never heard of them failing. and they are a real b**ch to get at.
a friend of mine had to do them on a rear wheel drive BMW. kind of a rare job, those bearings often outlive the car, wait until you hear noise before doing them just as a matter of maintenance. . .

perhaps some other guys can offer advice on lifespan for the rear ones.
i'm just relating my experience with the centre drive shaft bearing.

good luck,