The only area that has been a little dissapointing has been wheel jam due to build up of crud around the brakes.
It happens with damp mud and dry-lake playa, too (see attached pic). I have often pondered what a change to discs would mean, and have concluded it is best for my needs to wipe/scrape the stuff off than to deal with (what for me in my use would be) the detriments of discs.
That said, I think disks are a wonderful solution to address rim-brake pack-ups, and that's why I specified a disc-compatible Rohloff on my Nomad Mk2. It not only future-proofs the bike, it gives another option for braking while keeping the same fork and rim brakes up front (which means I can also keep the same lowrider rack option as I have at present with a rigid, v-brake compatible fork).
Andy, I'd think a spare fork, properly designed and fitted for discs would be really appropriate for consistent wintry/snowy use. A person could make a semi-annual swap, along with the tires.
All the best,
Dan.