If you find Rawr too intimidating to use, I'd like to humbly offer my spreadsheet as a simpler alternative.
Simple Bear Mitigation Spreadsheet | The Inconspicuous Bear and use the EP values to make your gearing choices.

The main decision you have to make is whether to use the TTL values or the Mitigation values for Stamina. My best advice is to use Mitigation unless you feel that you are getting gibbed by bosses at your level of content.

I am not sure I agree with threat being a non-issue and that stacking stam is acceptable if deemed necessary without any threat issues.

While working on Nef and now that we are working on Heroics, I have been forced to stack stam and dodge in order to survive. I am having terrible threat issues and I was wondering if other heroic raiding bears were seeing any issues at all? I can't understand why I havent heard about this anywhere else, but everywhere I read everyone is saying "threat is a non-issue and can be completely disregarded". Problem is most of the people saying this havent gotten past 9/12 or 10/12 normal mode and all seem to be stacking agil yet. If I single target focus on threat I can just stay ahead of DPS, if I need to tank more than one target I run the risk of losing one of them. We are currently working on Halfus as an example. I am activating and tanking the Storm which is our first kill target. I am also tanking Nether which is MD'd to me. We are tanking on the whelp cage and stacking all of the drakes/whelps and Halfus on top of each other for maximum aoe splash damage. I activate the storm, pop barkskin and FF/Mangle him when he becomes aggro. I then start lacerating to get pulverize up until FF is up again and toss a demo in there once both drakes are to me. Then I switch to the Nether and FF/Mangle it, but that is all the time I can give to it before switching back to Storm or else I lose it. Some times I will lose the Nether to the mage if he gets good RNG on his AoE (we have him pulling 50k some times and 150k others). We have even resorted to starting on Halfus for a few seconds to give me a lead on threat.

Anyone have similar troubles? I have actually reforged hit back into my gear and reforged the "other stat" instead just so I can minimize my misses early in a fight while I am ramping my threat.

Threat being a non-issue is outside of the first 30 seconds. Every tank has issues within that window without a Tricks/MD. Thrash out-threats Lacerate pretty early on, and you should be using it on CD. FF is also minuscule threat compared to every other ability you have. It should only be used when you're low on rage (which should rarely happen unless you get a severe dodge streak).

Threat is mostly a non-issue for me simply due to Berserk. To Natasmai, you talk of tabbing, stacking Lacerate, Pulverising - why is Berserk + Mangle spam (even of you tab between your two targets to make sure it hits) not working for you?

If you position correctly and/or ask for 10s before the Whelps are released you should be able to get a good number of Mangles on both Drakes which is a pretty decent head-start on any DPS that is AOEing.

If you're really THAT hard pressed for threat (no such issue for me even using stamina gear, and I don't think we magically lose 30% threat going from normal to heroic), reforge into expertise since it basically gives double the benefit of avoiding misses (by mitigating dodge and parry at the same time) except in the spell interrupting department.

While you can't guarantee which target you hit with the splash, an aspect of berserk you are missing is that it lets you mangle spam. Simply swap between the two drakes as you mangle and you should be fine. That is one of the big changes that bears need to get used to again, just relying on aoe and splash abilities doesn't always cut it these days. It fell out of style in Wrath but I would suggest to most bears to try mouse over lacerate and mangle macros, for example:

I think you mean "harm" instead of "help" in the cast conditions.

Stamina's only purpose is to survive burst damage - once you have enough stam to survive a worst case scenario, your time to live is the same unless you have enough stam to survive another melee hit. Stamina is further devalued by the way healing has been designed for this expansion - for the Nef fight, tanks are receiving on average of 4-6% overheal, meaning that for the vast majority of the time, tanks are not at full health, and any addition stam you have has literally no affect on your survivability.

On the other hand, agility is a mitigation and avoidance stat, giving crit, AP, dodge, which contributes to savage defense uptime and absorb amount (an attack that is dodged also means that SD will be up longer).

From my experience, and from fiddling with rawr and other tools.

When you are breaking into a tier (normal or heroic or new tier) with the previous tiers loot then stamina is king.

Once you have a foothold in the new tier and a reasonable amount of the new tiers loot (3+ pieces), then Agility reigns supreme.

Consult Rawr or similar for specific values. Stamina does have it's place and role, but it's value is exceptionally variable.

It looks as though it is confirmed that us bears will be having some threat nerfs shortly: from the 4.0.6 patch notes:

# Lacerate damage has been reduced by approximately 20%.
# Mangle (Bear Form) weapon damage (at level 80+) has been reduced to 235%, down from 300%.
# Maul damage has been reduced by approximately 20%.
# Pulverize weapon damage percent has been reduced to 80%, down from 100%.

I don't think we can be surprised with the threat nerf with the damage that bears were able to put out.

However, I'm kind of surprised that there are no survivability changes in the patch notes. I was under the impression that druids were underperforming in that department, and expected at least a token buff.

Are druid tanks doing better than I believed? The new agility focus has given us a good lead on avoidance over other tanks, but at the expense of a noticeably lower health, as well the other tanks seeming to have more reliable masteries. Is our dodge just that good? Or is our mastery actually competitive?

Has anyone actually been having problems with threat? Other than maybe at the 30 seconds mark when misdirections and tricks fall off I tend to be so far ahead of the DPS on threat that it is a complete non issue.

In fact since Cata, I can't recall ever seeing anyone pull threat at any time other than during those first 30 seconds, which you can just berserk during.