Seeing as my Horde guild is just getting around to do Onyxia, we're all involved with the Ony key quest line lately. And last night (on my newly built PC-- hawt!), a few guildies and I went through and did the "Test of Skulls" quests. If you've never done them, you're probably Alliance, and just this once you can consider yourself lucky. Not because they're hard (they're not, especially with a full party of 60s in epics like the one we had), but because it is, shall we say, "travel-intensive." You go to Dustwallow, down to Tanaris, up to Winterspring, out to Swamp of Sorrows, back to Dustwallow, Wetlands, Dustwallow again.. well, you get the picture. We traveled around the world for about two and a half hours or so, just to kill four dragons.
Traveling has always been one of the big reasons why MMORPGs are such a timesink, and World of Warcraft, while mitigated a little bit with the hearthstone and a few gameplay mechanics (we didn't have a mage in our party last night, which would have helped out a little bit), is no exception. Especially before you get your mount, travel is pretty much a chore that most players /afk away from as much as possible.
And it's not like there aren't better methods out there. Elder Scrolls IV (which I'm also playing on the new PC) lets you click-travel anywhere you've been, and even some places you haven't. And I haven't gotten a chance to try Guild Wars yet, but I believe they also let you visit anywhere you've been in just one click as well. So why hasn't Blizzard followed suit?
I agree there are a few reasons to take things slow. Exploration is just as fun as fighting, and without traveling everywhere, you'd never see the world. And speaking of seeing, there's a certain thrill in flying on the griffon anyway-- the flight from Stormwind to IF is particularly pretty. But after the 156th time or so, it gets a little old. I don't play this game to fly-- I play to fight. And every second in the air is a second spent not earning XP or gold. So why is traveling such a travail?