My first post is going to deal with gray loot, having big bags & making the most of your limited game time (yes, these things are linked together). I've always been the type of player who looted every item that dropped, and was ready to vendor it after a play session. It was a habit I always had. So when grouping with people in my guild recently, I was fairly shocked to discover many of them never looted gray items. I also noticed in PuGs that many players would leave gray loot, which I would then scoop up.
Typically, if I'm reputation grinding Netherwing or Shattered Sun for an hour, I'll get a couple of gray items at least which could add upto 5 or 10 gold. Now say if I spend 2 hours a day on dailies (or even better leveling in Outland), that's potentially 140g a week. It could be significantly more if your spending time questing in Outland. That's a huge amount of money to be throwing away long term. It's certainly a nice way to cover your repair and other maintenance costs at minimum. Personally I find it a great source of income, as I don't spend all that much on repairs.
Asking people why they don't loot gray items, I'm often faced with the same answer; I just don't have the bag space. The same people however often have 16 slot bags, which for anyone level 70 is a poor effort. Having large bags for me is an investment every WoW player should make. Earning the 40g to buy an 18 slot bag off the auction house, is about 30 minutes worth of dailies. A small price to pay for something that will make you time and money. If you upgrade from a set of 16's to all 18 slotters, thats 8 gray items you may have previously left unlooted. Vendoring these items soon adds up, and soon the 160g spent on the 18 slot bags has turned into hundreds more.
I carry 20 slot bags with me, which set me back 400-500g each, but I feel it was money well spent. Looting everything you see is not the only way you're making money out of having large bags; you're actually buying time. Say you spend 2 hours a night questing or farming, and you have a set of 16 slotters. 30 minutes in your all out of space and you have to run back to town to vendor your trash, or mail stuff to your bank alt. Meanwhile the extra 16 slots I have mean I've gone uninterrupted for the entire 2 hour session. Again this time all adds up.
The next patch update will see the introduction of 22 slot bags priced at a massive 1200g. I'm probably going to buy at least two, but most likely I'll get four for my main. That's 600g for one extra slot, so it will probably take a long time to make any return on that investment (if at all, Wrath of the Lich King will probably introduce a 24 slot bag before I get the chance t0), but I have the funds to indulge myself. However, this post still serves as a useful tip for lower level players. You might be new to the game, in your 30's and still carrying 6 or 8 slot bags. You can buy 14 slot bags on the auction house for just a couple gold, which really is not a huge amount of money, certainly achievable. Soon your first mounts will be available at level 30 for a mere 40g, and maybe the 60g saving will encourage you to spend money on 14 or 16 slot bags, which will certainly make your leveling process towards Outland more enjoyable, easier and maybe you'll end up a little richer along the way.