I haven't done any reforging yet. Nevertheless, I have some Thoughts:
1) Stamina is still king
You can't reforge primary stats, including stamina. You can reforge everything else.
I actually think that reforging therefore narrows gearing choices, since in a world without reforging you might have wanted some threat stats such as hit on a gear item, or defence, or in the bright and shiny Cataclysm healing model a ton of +dodge rating might have been superior. You might therefore have worn an item with these stats. Not so now - you can get your threat stats, or your avoidance, by reforging. You can't get stamina so it will still be the case that stamina is better than everything else.
I imagine that there will be a similar rule for most classes where the most useful gear attribute is a primary stat.
2) How much hit is still needed?
**Caution, what follows is based on my understanding of hit mechanics, which is a little rusty.**
The glyph of taunt has gone. I've got about 6% hit I think, which means that since taunt used to use the spell hit table I would therefore think that I had 11% chance of taunt missing a boss. I have not had a taunt miss yet (2 raids so far) so I wonder if the developers have simply made taunt hit all the time, which is something that GC said he might do.
The reason I am musing on this (aside from worrying that I'll miss a tank swap) is that since as a threat stat expertise is twice as good as hit, and I am under the expertise soft cap, perhaps I should be turning some of my hit into expertise. I don't want to do that however if I'm going to muck up my taunting.
3) What is the parry diminishing returns curve?
Dodge, for me, is not as good as parry. Dodge avoids the next attack, whereas parry avoids the next attack and procs Hold the Line. Parry is therefore better.
However, on live pre-4.01 parry had a much more severe diminishing returns curve, meaning that you needed more parry rating to get an effective 1% of parry than you needed of dodge to get an effective 1% dodge. I wonder if that will continue into Cataclysm - if so, it means that gemming and reforging and enchanting dodge will still be better than stacking parry. If not, it means that dodge will be unquestionably worse than parry for me in the expansion.
I still therefore don't really feel like I have enough information to go out and pay cash to change my gear via runeforging. It might be different in Cataclysm if survivability is a massive issue, so we're adding avoidance to everything at the expense of threat, but at present I hope that some clever people at Tankspot and EJ will apply their ginormous brains to get an idea of the mechanics of tanking in Cataclysm.
EDIT - Ah - some of the information may be here.