I replaced the switches and haven't had any problems with the unit. Before, hitting a switch would occasionally not activate the pedal, but the replacements fixed that problem. From what I've seen, the only reliability problems people have had with the pedal is from the switches. So if you replace the switches, it seems unlikely that it'll just break down on you.
I haven't had the switches replaced, though I had mine modded for the volume drop mod, the double preset switch and a custom exterior. I've never had a single problem with my DL-4 and have had it for over 3 years now.
Ok, as an update, it broke, although I don't think I should blame the unit. I left it plugged in overnight and in the morning it suddenly didn't work. I traced voltages for a bunch of diodes, ICs and other usual suspects, but I still haven't been able to find out what's wrong. I think it got hit with an electrical surge, which honestly, isn't really a knock against the pedal's reliability. Anyway, it has been reliable for 3 years until today.