I posted this a couple of months ago:

Very strange thing happened while I was riding home the other night- my rear wheel suddenly locked up while I was accelerating after stopping for a traffic light. Hadn't picked up much speed yet, so the stop wasn't dramatic, but definitely a surprise. My first thought was that a brake shoe had somehow planted itself on the rim, but soon found the wheel bearings had seized hard. I couldn't turn the wheel at all by hand. I was 3 miles from home and it was late, so all I could do was loosen the Q/R on the wheel and walk the bike home, with the rear axle turning in the dropouts the whole way. A kind soul stopped and gave me and bike a lift for the final mile.

Next day, I removed the freehub and took the bearings apart. Turns out the cone had come loose from the locknut on the drive side of the axle and had spun until it mashed the balls tight in the race. The axle threads were all trashed, so I had to install another wheel. In the meantime, I've saved the original wheel in hopes of finding an axle that will work with the rest of all the bits. I think the failure resulted from me packing too much grease in the bearing after a recent overhaul; some had leaked out onto the axle and probably caused the cone and locknut to slip.