Start heroics when you can do around 1400 dps. Start 10-mans when you can do around 1500 dps. Start 25-mans when you can do around 2000 DPS. Some folks probably will disagree with these numbers, but the thing to remember is that it's ultimately up to the raid leader. These figures are only for boss fights too. If you're being judged on trash DPS, then something is probably fundamentally wrong with the raid you're in.
Additionally, you do no DPS if you're dead. That means you need to know all the fights before you enter the instance / raid. If you die, you do zero DPS and are a prime candidate to be replaced.
"Whatever happened to epic gems?"
Grab a Stormjewel from the fishing daily, but other than that, you'll need to wait until at least the next major content patch.
"Does Blizzard have any plans to make spawned quest mobs auto-tagged?"
That'd be nice, wouldn't it? I recommend posting in the Blizzard Suggestion Forums and hope that it gets someone's attention.
Mused Moose asked...
"Did Blizzard remove the 'Bloodsail Admiral' title from the achievements?"
The achievement is a Feat of Strength, so you can't see it.
Mused Moose also asked...
"Has Blizzard said anything about adding Jewelcrafting trainers to the non-expansion cities?"
I don't really think there is a need. Everyone congregates in the major cities as is, and everyone has Dalaran either set as their hearth or can get there quickly. But no, they haven't said anything about adding Jewelcrafting trainers to other locations.
"Didn't the interview a few days ago have a Blizzard staffer saying the Argent Tournament expanding was the biggest feature of 3.2? That leads me to believe that there won't be a raid if a world event is the largest piece of content in the patch."
I think you're reading too much into what Blizzard has said. While there Patch 3.2 will feature a bunch of Argent Tournament stuff, it'll also feature a lot of other things. Remember too that Blizzard has different teams working on things, so the argent tournament team is very likely separate from the instance / raid team.