I did some mining this morning and got 4 gems, yay! Kind of nice since I've gotten zero gems the last couple of days and I've been trying to collect 30-40 ore every day. So I sent those off to my Jewelcrafter and she also found some reasonably priced gems on the auction for 2-4 gold each. Even though I had no orange recipes at 320, I was still able to use the green and yellow recipes and get 4 skill points from 6 gems. Considering that the jewelry you can make at this point requires 2-3 gems and some Fel Iron, I think it makes more sense to stick with gem cutting for this range.
At 325 you get 4 new gem cutting recipes and some sort of component recipe. I haven't made it yet, but it appears to use the by-product dust from prospecting ore and some of the bonus drops from mining. The finished item, called Mercurial Adamantite, is then used as a component in other jewelry recipes.
One disturbing discovery I had was that all of the new recipes I got at 325 were instantly yellow. The Azure Moonstone Ring recipe I learned at 320 is still orange, so I find this an odd move from Blizz. But whatever, I went ahead and cut more of the gems I had and got a skill up for each one despite the recipes being yellow. There are no new trainer recipes until 335 and then nothing at all beyond that. So we'll see how far gem-cutting gets me =)