I have had DCS for about 4 years or so, got it right when the Rev L TIU came out (whenever that was), I have had Legacy since early last Sept. or a little over a year. Had to wait on that delay with a part problem or whatever that was, had ordered it a year earlier.
DCS : The thumbwheel on my DCS remote broke, it was the plastic bracket that holds it in place. However it was never really non-functional, I was still able to use it and run trains with it. I was able to shim it up with a piece of wood and hot glue while I waited for my replacement thumbwheel from MTH. I got the new thumbwheel but didn't replace it right away, my wood shim worked well for a couple years or so. Finally replaced when I dropped the remote and it dislodged the shim. It was an easy fix, worst part was opening the remote and getting everything lined up again to put it back together. Still using it today and it works very well.
To be fair here, this was probably somewhat self inflicted as I was pressing a bit hard on the wheel at times. I have lightened up since, but the thumbwheel is probably somewhat of a weak link on the remote. However, it survived my dropping it very well. While I was watching it hit the concrete floor, I remember thinking it was going to be time for a new remote, but it came through without a scratch.
Legacy: Remote is still working just fine, no problems with that at all. However, the base had to go back to Lionel because it would not update. No problems with the remote updating, that worked just fine. Lionel fixed it and all is well now. Updated it again just a few weeks ago.