Logged in to my normal user account: C:\Users\tejón\Gaslamp Games\Dungeons of Dredmor\mods\any-given-mod.zip ...does not appear in the Mods list from the launcher. Using a special account for testing this, since I had a similar issue with Civ 5 on release: C:\Users\boof\Gaslamp Games\Dungeons of Dredmor\mods\that-same-mod.zip ...works fine. Incidentally, the last.txt issue described here is not affected. Whoops, forgot the tag: Win7-64. Also I should mention that it doesn't matter whether the mod is zipped or in a subfolder (verified both working on boof, neither on tejón).
Maybe it's related to the special character in your name of tejón. I've not had any issues myself, but that is more than likely because I have XP, 32bit, and I don't have umlats in my name. I'm not fully up to speed on issues games may have, but I always thought special characters can cause problems for many things, not just games, so maybe it really is something that simple.
Well yes, I figured that was the cause. That's why I said so in the thread title. Good to know it's already on the list, anyway.