only if you've been idling in Dal

@thegatherer

Don't you get rested everywhere? Just incredibly slow if your not in an inn / city?

We didn't with WotLK. Or at least, you didn't start accumulating your rest bonus until you installed the expansion. I believe that rest is an overlay of your EXP bar, and since you don't currently *have* an EXP bar, those little ZZ's on your portrait aren't actually doing anything for now.

I can see that my 80s already have some XP on their bar. What I would like to know: in Cataclysm, will one level be the rough equivalent of a level in vanilla and BC, or about equal to one and a half levels, or equivalent to 2 levels? Considering the blahs some people are having now toward the end of this x-pac, what will people do if they level in a few weeks to max level? Won't end game come sooner along with its attendant raid burn out?
And: Why, every time I look up at the night sky in Azeroth is there ALWAYS a full-moon? Not a new moon, not a quarter-moon, not a half-moon, but always a full-moon. Doesn't that play havoc on the Azerothian tides?

I dont think anything has been said on this. However, given the number of zones, its probably safe to say the time to level will be about how it is in Wraith, about 5 hours without BOAs and about 4 hours with BOA, assuming fully rested.

I can see this as potentially sucking, they are only adding about 20 more hours of game content for the end game. Hopefully they can push the next xpac out in a year rather than 2-3 years, since most people have 80s and that run to 85 is going to go quick.

But as mentioned we don't know anything for sure. It is possible they will make us grind mobs for 4 hours per level since the quests have dried up (extremely unlikely, but possible).

Ah previous comment was @Rod (wtb edit). And i forgot to answer the original question.
@Salty, what you had in rested XP when you dinged 80 is what you will have when you buy the xpac. That's the way its been for vanilla and wraith. You do not get rested XP at level cap, so all that standing around in dal did nothing for that purpose. If you had 0 rested XP when you dinged 80, you will start with 0 rested XP. If you have 150% rested XP, you start with 150% XP.