I just read this post on wowInsider talking about how much it costs to skillup each crafting tradeskill. Here’s a copy of the chart they created. (Note: There were too many variables for Jewelcrafting from 300-375 so there’s no red bar.)
You can easily see what skills really cost you in the game. Not to mention the cost of all the annoying loot arguments that tradeskills can cause. I guess my only comment about that is Alchemy looks like a pretty good use of your hard earned gold, since they also have some profitable potions to sell on the AH.
Now take a second look and ask yourself “Will I every make 4000g from blacksmithing?” No. What are you stupid? Now number 2: “Are the BoP items I can make from blacksmithing worth 4000g plus the price to craft the BoP.” Well, seeing as I’ve never seen an epic on the AH posted for more than 2500g, I’m going to say “no.” Now it might help you get that first raiding spot or something, but I think there are other ways to improve gear that do not involve all the time, money, and effort that a tradeskill does.
I would like to talk a bit about something else this shows. Who the biggest suckers are. That’s right. If you want to makes some g, it looks like you should really invest in mining to get some money off of blacksmiths, engineers, AND jewelcrafters. You can also see that if you make it to 275+ in enchanting you can make some pretty good money off your fellow enchanters trying to get to 375 (which I did and can attest to the profit). Skinning for leatherworkers isn’t a bad choice either.