I already have an external display, I had to buy it as I couldn't trust the iMac panel! The only question is, do I wait or buy now.
That's a pretty fair question. Since there's a decent number of us who need to update our kit to stay plugged into Apple's ecosystem. Leaving aside the Mac Pro vs iMac question, there was a brief rumor pulse that there would be a Mac Pro update with the Lion drop. But that actually turned out to be a MacBook Air / ThunderBolt Display release.
Apparently Thunderbolt capable next-gen chips are not available from Intel yet. So we should probably not get our boxers in an uproar till at least Q42011, but on Apple's MP timeline, that might even be sometime in 2012. The last upgrade cycle was 511 days -
a year and a half. The one before was 420 days.
Patience, Grasshopper.
What concerns me that on the current arc, we perhaps should check our expectations. The last update was kind of "meh"... We'll certainly get Thunderbolt, and of course a CPU bump, they'll be SSD's and maybe a nudge up on graphics cards. They'll
probably still have optical drives.. maybe. But they're days are absolutely numbered. Don't hold your breath for USB 3, eSATA, or gods forbid, Blu-Ray... Apple's just not interested. But at least with discrete graphics cards, you can still plug in third party displays. Not so with the thunderbolt equipped MBA.
But otherwise, I am expecting essentially the same machine in most respects. And still a costly beastie.
If you NEED it, go ahead and buy, you'll get Lion too, now. But if you can wait it out, you can wait for the new model.