My first character on the European WoW servers was my warrior, and that was also my first character to reach level 60. But then I leveled a second character to 60, my priest, and due to healers being always more in demand for raids that priest became my "main", my raiding character. So in the expansions I always leveled the priest up first, and then the warrior in case a tank was needed, as "Plan B". That never really worked in The Burning Crusade. Nevertheless in Wrath of the Lich King I still leveled up my warrior to 80, and having too much gold anyway, equipped him with 8 level 80 epics which were bind on equip, most of them crafted. But up to yesterday I just did one single heroic run, and one Vault of Archavon run (which by extreme luck netted me another 2 tanking epics).
So last night I had my priest at the Naxxramas meeting stone at our usual raid time, the raid leader invited everyone interested in raiding, and among 18 possible raiders there was just one tank, and several healers. So finally the Plan B kicked into action, and I could go with my warrior as off-tank to Naxxramas10. And that was a big success, and great fun. In spite of me being new to that off-tank role, and there being another raid newbie in the group, we cleared the abomination, spider, and plague wings of Naxxramas. I was quite happy that in most cases I was able to do the job satisfactory, there was only one boss fight where I ended up dead. And I not only gained a "I survived Patchwerk" bumper sticker, but also the T7 leggings, a tanking ring, and a staff for "off spec", when I want to go dual-wielding two-handed weapons as second build after patch 3.1.
Doing the same raid in a different role was great! Part of the fun was the increase in challenge, switching from an overgeared priest who had done all of these fights as healer multiple times to a not-quite-as-well geared warrior new to the off-tanking job. Of course being not-quite-as-well geared also has the advantage that you're more likely to still find an upgrade. But another big part of the fun was seeing the same old encounter in a totally different light. Doing the same boss in a different role is nearly as good as doing a new boss, because you end up watching a very different part of the fight. Instead of the usual healer's tunnel vision on health bars I suddenly needed a lot more spatial situational awareness, finding the adds and tanking them. That not only was very interesting, but I think I learned a couple of things about these fights that I wasn't totally aware of as a priest, and that might make my priest a better healer.
The only negative point of the whole off-tanking Naxx experience was that there are some bosses where the off-tank isn't really doing anything, except hitting the boss with some ridiculously low dps, and being ready to replace the main tank if he dies. What is an off-tank supposed to do at Maexxna or Loatheb? I'm not even sure the dual spec feature would help here. Would you want the off-tank to go full dps for these fights and end up *not* having a backup in case anything goes wrong with the main tank? I'm not talking about uber guilds who never ever have a single death in raiding here :), but your average raiding guild, where sometimes things go wrong, and a good recovery prevents a wipe.
Anyway, Plan B of having a reserve tank in stock if ever one was needed was a full success last night. And of course the fact that the starting raid dungeon in WotLK is much easier than the starting raid dungeon in TBC was enabled this success. So while I can see how some people are starting to get bored with WotLK raiding, and I'm kind of waiting for Ulduar myself, I still claim that Naxxramas has the right difficulty level for a starting raid dungeon. The only problem is Blizzard not providing more than that starting raid dungeon plus a few single-boss raid dungeons sooner. It is a perfectly good idea to offer bicycles with training wheels, there just has to be bicycles without them as well.