Well I sold my first cut gem so I used the funds from that to purchase another recipe (Lustrous Star of Elune, +2 mana/5 sec and +4 INT). I had one Star of Elune that I prospected this morning, so that's three rare gems I've cut so far.
I also read on the beta forums yesterday that there's a prospecting bug which allows you to get unlimited skill points prospecting the same stack of ore over and over. So I thought I'd see if I could take advantage of that... errr duplicate it for testing purposes. I went to Arathi and mined about 50 iron ore, but no dice. I did however note something else, every single prospect I did produced a gem and 4 (out of 10) gave two gems. Obviously this is just a random sample, but it's possible that prospecting lower level ores gives a higher success rate than prospecting ore that is equivalent with your jewelcrafting skill.