Just thought I'd drop in to say that I've finally moved on to the new version (having finished up my previous 40d fort), and that I will be making an Orc mod for DF2010. That said, combat (and training, and wound recovery, and etc.) have all changed quite a lot from 40d, and so balancing it is proving a bit difficult.
I'm fairly sure, for example, that it's not possible to take on the first Orc siege if they are progress trigger 1: My test for that is embarking with six military dwarves, an armorer, and the materials to make everyone full suits of armor, which is looking like it's not viable. Both the armored war elephants and giant wood spiders needed a bit of a revamp (oddly enough because they weren't being deadly enough - the new skin/weapon interactions seem to make unarmored creatures very vulnerable), and while I can test a certain amount of it in the object testing arena (THANK YOU TOADY!), some things really can't be tested other than by getting thirty orcs to attack a forty-dwarf fortress.
To reiterate: There will be DF2010 Orcs. I will be doing my best to balance them, so that they are a challenge to experienced combat players but not insurmountable with proper preparation, leading to rewarding fights and epic tales. Hopefully, I'll be able to release a beta version in the next month or so, especially as I become more familiar with the new tools at my disposal.