Same here. MUDs got my unix / network / C programming up to par (and to this day, decades later, I still work in the field). Incidentally, "my" MUD still runs (some 25 years after its start), although it's not thriving by any means. More like 2-3 concurrent players at a peak (we used to be small anyways, our max concurrent players peaked at some 40 in the late 90s and early 00s). There's still new people picking it up and raving about the depth of content in it though, so at least that makes me happy :)