Although current 1.0 users can download the 1.1 upgrade, it's impossible to buy 1.1 itself. The Apple store I contacted in the Portland area estimated arrival by mid-May.
And although 1.1 will indeed be $299, you cannot purchase 1.0 for that price. You must still purchase it off the shelf for the full $499, then get your "e-Coupon" -- which, by the way, is good only for one item valued at $200 or more at the Apple online store. Don't expect to go there and use your coupon towards the purchase of a bunch of cheaper items.
I really like what I've seen of Aperture, and I want to buy 1.1. I'm just a little frustrated at the complexity of the situation (and the fact that neither the local Mac Store NW nor the official Apple store knew any details of the real policy).