4-5 of our ex-guildies re-rolled Horde on Twisting Nether around December last year. Well technically, they started playing WOW again after selling their Alliance chars in our guild.
They hit 70 and started raiding with their RL friends around January, some Kara, etc. and then killed Gruul for the first time on 24th January.
Sneakattack DKP DKP: Raid Summary
They killed Illidan for the first time on 25th February.
Sneakattack DKP DKP: Raid Summary
They killed Brutallus last week.
Now admittedly, some of their chars just "appeared" as lvl 70 on Twisting Nether so they either bought new or transferred most of their existing lvl 70 chars, I don't know - but this is basically 25 people without raid items and none were attuned to BT.
i.e.
Dynn - WarcraftRealms.com
They religiously farmed badges, Kara and ZA. Their locks and mages used the still-good-but-low-on-stamina craftables, and everyone farmed PVP/Arena weapons. Kinda inspired me to push Tier 5 alt content within our guild, pre-2.4, based on how quickly you can progress. Having said that, they wouldn't have been able to do this as quickly without having other guilds that they could buy/borrow HoD from.
They aided their progression by giving all tanking items to their MT.
To summarise - all you need is the opportunity. To kill the Twin Eredar, we ended up taking some alt resto shamans through ZA/BT and throwing loot at them. They got some nice items very quickly.
There's a total lack of decent Resto shamans on alliance and recruitment is near enough impossible. I doubt we're the only Alliance guild to do this. We'd certainly do it again for the right candidate if they were able to prove their ability and worth.