I'd still sell what you can, rather then stockpile.

You're better off with a pile of gold, then a bunch of previous expansion gems and such.
I'm not saying Cataclysm will be next week or anything like that, but it's coming.

If you want to play the Undercut game, get Quick Auctions.
I've got it set, very simply:
a) My max price is 237g, which I list at if no one else is listing the cut.
b) My undercut value is 1c.
c) My minimum price is 125g, so it will not list anything under that value, gems below 125g get listed at 237g.
d) Auctions are listed for 12h, for the minimum listing fee.

I then periodically while questing, heroic'ing or pvping, in between dungeons/battles etc, log the auction toon on.
Hit Cancel, to cancel anything on which I've been undercut, that I can also relist for somewhere in the 125-237 range.
Visit the mailbox and pick stuff up.
Return to the auction house and hit Post.
Then log the previous toon back on, and resume whatever I was doing.