Yeah, I've read about that. My guess it's that it will be some phasing thing for level 90s and it won't affect low levels (both Horde and Alliance still need to level up in Northrend).
With the new mixed inter-realm zones I've noticed many F2Ps in the Ragnaros + Drakkari Goldshire (both Latin American realms). For some reason QT are not mixed with us (maybe because QT is a normal server, not PvP).
I don't think you'll be able to use this free 7-days to get Brewfest mounts though.
This promotion ends in 19/09/2012 and Brewfest begins in 28/09/2012.