The announcement earlier in the week that Blizzard was allowing free transfers from a couple Oceanic PvE realms to the Oceanic PvP realm Thaurissan lead to a storm of speculation that Blizzard could be considering opening up PvE to PvP transfers on a wide scale.
Blizzard has recently said that they won't be allowing large scale transfers from PvE to PvP servers. This rule was supposedly in place for a number of reasons, the main one of which has always been the relative ease of leveling a character on a PvE server compared to that of a PvP server. Having done both, I can say that it wasn't too different – a few more tricks had to be used when leveling on the PvP server, but in no way was my leveling prolonged on the PvP server because of the PvP elements.
Drysc chimed in on this very topic yesterday.