Top 3:
1) Joining forums was the first/best thing I did. I started on Realbeer,com, then the BN, and now this forum are where I go for my daily fix of great Brewing info. Along with this were the BN podcasts. All that info coming from the likes of Jamil, Tasty, Palmer, Nate, and the forum stars like Denny and Martin, all made me a much better brewer.
2) Becoming a BJCP judge. I thought I brewed pretty good beer. All my neighbors loved it. So, I figured I'd enter some competitions. All I kept getting were high 20's and low 30s. What are those guys tasting that I am missing? So, I studied and became a judge myself. Sure enough, I figured out what I was doing wrong and my beers got better and better. This was around the time that JZ and Plise were doing the Style shows.
3) Co-Founding my homebrew club and becoming involved in WAHA. All of the online stuff was great, but getting in with other brewers in person was so much better. We have a thriving homebrew scene up here in WA largely because of WAHA and the personal connections we formed through it. I've made friends with so many homebrewers across the region as a result of our statewide events that only came about because of WAHA.
Bad:
1) 5.2. Enough said
2) I way overdid it on gadgets like sparge arms, etc. Ultimately, I simplified everything back down, and am much happier for it. Thanks, Denny!
3) The whole "more has to be better" movement. I tend to like smaller, simpler and cleaner, over bigger and over-the-top now. I think we are seeing the second peak (like a double-top in a stock chart) with these NE IPAs on the heels of the prior Black IPA craze or the IIIIII-IPA craze. They can keep it. i'll stick with my Helles, Vienna, Kolsch, or hoppy Blonde.