Qiraji mount from AQ40 was pretty sweet. Not only did it look pretty cool, but the idea of summoning a giant bug to burrow up through the ground and allow you to ride it was fun too.
Unfortunately, ever since the Burning Crusade came out, my poor, poor bug has wasted away in the bank. I have been haunted by the thought of it being so lonely in there ever since. I can't even watch Starship Troopers without feeling nostalgia and a twinge of guilt to imagine good old bug-bug waiting forever to be ridden again. I honestly do think that if they ever removed the restrictions on my bug, I'd ride it everywhere. I suppose it might make a few Scarab Lords feel a bit less special about their ride-anywhere battle tanks, but... come on, they get the BLACK color, and that's totally unique enough by itself, right?
Unfortunately, it doesn't matter, since Bornakk chimed in on a forum post praising the bug mounts today to say that they don't plan to let you use the crystal outside the instance any time soon. He did suggest that you could use it to link in chat and taunt people who never had one. I say I'd rather ride mine. I'd even do a big old quest line or pay 2000 gold, like some of the people in the thread suggested.
On the plus side, he didn't say they'd NEVER remove the restriction, so maybe there's still hope. Hey, if nothing else, we'll probably be headed into Azjol-Nerub come Wrath of the Lich King, right? Considering we'll likely fight bugs there, maybe we'll be able to use our crystals in there, or at least tame some new mounts.