These guys are dead on. SMAW (MIG) welding carbon steel isn't *that* hard to do (but not necessarily as easy as your first practice weld may suggest), and it's really handy skill to know. However, welding up stuff that touches beer is a whole other game. You need to be good at tig welding thin metal, you have to back-shield, etc. I just got four half-barrels that are destined for keggle-dom, but I'll be using weldless fittings.
That said, I took a couple classes at the local tech college. The first one was a basic Intro to Welding where we covered stick, mig, and tig welding. It was $85 for 10 weeks of class, which was totally worth it. Then I took a for-credit class on SMAW welding mild steel, which was a lot more comprehensive (including multi-pass and out-of-position welds). Even that class was only $230, and I could have gotten work to pay for it as continuing education. I am very, very happy to have done this...I don't weld often enough to be *really* good at it, but I'm good enough for anyone who can't weld on their own. I bought a welder, but you can rent one for a weekend or whatever. Or, if you get in good with your instructor at the tech school you can use *their* equipment. Any good tech school teacher will approve of projects like this, especially if there is a beer involved at the end.
At any rate, the cannon that we built after learning to weld was *awesome*.