In my experience with both mountain and road wheelsets (both Bontrager brand), the cartridge bearings seem to last forever.

I liked the old cup/cone hubs, mainly because I derived some sort of perverse thrill of cleaning, packing and adjusting the bearings.

However, in the past 6 years with the cartridge bearings, they've been maintenance free.

I guess that means more ride time, but I miss the intimacy of adjusting the hubs just right.

Ride on!