If you already have toons on your accounts.
And the accounts are upgraded as far as you want them.
Let's say, Classic + Burning Crusade + Wrath of the Lich King + Cataclysm (not out yet).
You could RAF link two existing accounts to two new accounts (which are Classic only, nothing else).
Then boost the four accounts... two keeper accounts, and two disposable accounts.
Once done, ditch the disposable (classic wow only) accounts.
And repeat the process with two more keeper accounts + two more disposable accounts.
I was going to ask that question. I have 5 accounts upgraded to LK, I want to RAF 2 more to get shammies and pallies. Can a reg account play with a BC/LK account if the new account stays in the old areas?

So bc/lk A links to vanilla C, A plays Goatface Shammy C plays Dwarf Pally ( I can never spell Drain eye)