I was recently approached about some gearing questions, following the 3.0 patch. Here's my current take.
Should I still choose to aim for 490 defense?
5.6% Critical Strike Reduction is still a requirement, and 490 defense is still the best way to get it.
Should I choose gear with SBV and SBR over other values?
Shield Block Value is now a great threat stat, particularly in situations where your tanking multiple mobs - and damage shield is kicking back 20% of it for every attack against you.
Shield Block Rating got a boost (its no longer worthless) - but its not something to be sought too hard after. Shield Block (the skill) give us the ten second window of all blocks (and super-sized ones, at that). For the other 30 seconds, Blocking will still be helpful, but its usefulness has to be measured in terms of [Avg. Boss Hit]:[BV] (as a way to reduce incoming damage), and compare that % Damage Mitigated to how much avoidance you could get (a common alternative on gear), and how much % Damage you could avoid.
Example: Fasty-McdualWield hits for 2k. With 500 Block Value, your blocks reduce 25% of damage. Whomp-Bigfoot hits for 8k, so that same 500 BV is only ~6% mitigation.
In the case where you could choose between 5% Block Rating, or 1% Dodge...
Over the course of 100 Swings
On Fasty: SBV Prevents 2500 Damage, Dodge Prevents 2000 Damage
On Whomp: SBV Prevents 2500 Damage, Dodge Prevents 8000 Damage
Now, this is a pretty terrible example, because the slow, large hits are going to be over a bigger period of time - but it should be enough to get you thinking that SBR isn't doing much for you against a slow-hitting boss.
Is HR and expertise still as important as they were before?
No. I use to keep myself near hit capped to stay above DPS in threat. But now, even after losing chunks of it to gear changes, my threat is still huge. It shouldn't be totally neglected, but its not as important. Expertise is worth retaining as much as possible, because its parry reduction still does prevent bosses from getting sped up attacks (even though damage, as a whole, is less of a danger).
Should stam still be one of the the most important values, even over SBV? (effective health vs. damage intake reduction+damage out)
Stamina still is king. SBV is great for threat/trash, but it isn't about to overtake good old fashioned effective health as far as boss tanking goes.