I've been going a little crazy with alt professions. As it stands, the only professions I don't have at the Grand Master level are Tailoring Alchemy, but that will be in the works soon.
Bank alt > AH for me. I'd rather ship something that may be of value to a bank alt for future use. For a time I was starting to question the wisdom of that decision, since I have two bank alts, each with their own guild and 3 tab guild bank, and they were all full. Then I got to leveling alts and their professions, and saved literally thousands of gold and/or dozens of hours of farming. Jewelcrafting, blacksmithing, and tailoring from 1-375+, gathering to fill the gaps between what I had on hand and what I needed, and buying from auction here and there when the gathering got overly tedious. I have a level 60 warrior with 430 jewelcrafting. My DK has 440 Blacksmithing at level 61. If it weren't for the wonky way they set up the level requirements for tailoring, my DK would be a GM Tailor...as it is, I'm stuck at 375 until I get my DK to 65, but at least I can condense the Frostweave I get here and there into bolts for future use.
I find that my need for gold is trivialized by my access to so many professions. If I need leg armor kits, I hop on my druid and make them. If I don't have the mats, I go get them. If I need food for raids, I can do that on my druid too (and spent this past weekend leveling her fishing so that I'm not restricted to farming meat). I routinely send stacks of Saronite to my warrior to prospect, and as a result I have between 6-11 of each of the rare WotLK gems on hand...just needs a quick request in guild for a JC to cut the one I need and it's done. In the process of leveling grand master professions, I get a ton of greens and even a fair number of blues that don't sell for much on auction but D/E quite nicely on another alt. Eternal Belt Buckles are easily made for a pittance with leftover Saronite and the over abundance of eternals I have on hand at any given time. I've got 20 Titansteel Bars in my pally's bank and no pressing use for them.
In other words, I'm self contained for the vast majority of whatever I need. Flasks and repair bills are easily paid for with a handful of dailies. I'm not wealthy by any stretch of the imagination...most of my toons have < 100g on them right now, with the exception of my pally (main toon) who has just over 5600g. That's plenty for my needs right now, and considering my next two alts through Outland/Northrend are already nearly capped or well on their way with GM professions, all they need to pay for is class and riding training.
I have no interest in things like memmoths with vendors or motorcycles. I'm not much for achievements in general, but even less so for those that would require hours upon hours of farming for rare drops (ie. pets) or paying hundreds/thousands of gold for them on auction. Once I've got Alchemy to the GM level and gold set aside for riding training, it won't be hard at all to divert surplus materials to auction from time to time, When you need to buy little (if anything) and have a lot to sell, the auction house is your friend.