The most IMPORTANT and useful threads for me were absolutely everything in the Safety forum. My studio wouldn't be what it is today if it weren't for Dale M and cheng076 - I know people sometimes get upset by the safety mavens, but I appreciate them telling it like it is.
From a skills perspective, I think the single thread that taught me the most was this Seahorse Tutorial from the Free Tutorial section:
http://www.lampworketc.com/forums/sh...ad.php?t=19127 - it touches on SO many skills, it taught me a ton. And it let me make something really cool for the first time.