Cataclysm will offer a new feature to this:

We’ve added a new flying skill called Flight Master’s License. When World of Warcraft: Cataclysm is released, players who purchase the expansion will see this skill available from flight trainers for 250 gold once they reach level 60. This new skill is required for flying around all Kalimdor and Eastern Kingdoms zones, including the new level 80-85 zones.

Dev post here

250 gold is trivial, even to 60s, so now, instead of mounted gankers patrolling, they’ll just fly over and drop in to say Hello. It should also make invading the other faction’s outposts much easier.

Rumor has it that Bliz once promised “no old world flying” or words to that effect. Guess they changed their minds.

Now, if you want to be the one dropping in to say Hello, then I suggest you get leveled up. In the event that buying the appropriate flying skills is a non-trivial expense then start with our gold guide. (Ok, when my Rogue hit 70, before Wrath, I had to spend some time mining and such to earn enough gold to get flying. You don’t have to. )

1. New Cataclysm Race – Goblins for the Horde!
2. Blizzcon 2009 News – Cataclysm announced