Remember that aside from hardware only features like Tessellation, DX11 is supposed to run on DX10 hardware. So in terms of quality, the DX11 jump is significant. Add in that the next gen consoles are going to be DX11 (from which many PC games are derived or co-developed), and you have a lot of weight going into DX11.
But the important thing to remember is that DX10 hardware won't be instantly obsolete either. You should get the same games to run just with the Tessellation option blocked out. And from what I'm seeing visually, that's not necessarily going to be the end of the world.
DX11 is very good to have mind you because a lot of games are likely to come in it's format when the consoles switch over. But 4870's and 280's won't be left in the cold either. I'd still wait the month or two to get DX11 either in AMD or Nvidia format, but don't go overly ballistic on anyone who decided they couldn't wait.
For me I remain unconvinced that AMD deals with quality issues in a speedy enough way. They've done the right thing with the driver program, so they get kudos for that. So we'll have to see how things improve with the new focus on drivers. Slowdowns in MassEff2, flickering still in many games is not yet fixed. But I remain hopeful that if they've started to churn out drivers quickly (like 10.4) that we'll see much more rapid progress in the future.
I also don't think 75% of folks are going to "wait" for Nvidia to go DX11 in June. That is a tactical error on Nvidia's part that is going to cost them the same way the desktop 5870 has - only worse because laptop purchases are usually made for a couple years time. Desktops buyers can be enticed with the next gen of cards, where laptop buyers don't change as easily (used sale/repurchase). So I tend to see a bubble waiting for DX11 hardware and then a slowdown. Nvidia won't sell much if they miss the bubble by 5-8 months.
So DX11 is good, and something to wait for, but not doom if you missed it and can live without it's features. I'm waiting, but not everyone need worry if they can't.