Go for it dude!!! (and for the Quad-Core version - damn I feel tempted with the Quad Core version)That 27" iMac is calling my name...
And as for me, I tried LR3, can't handle it. Feels the UI is horrible. Prefer Aperture UI that seem to be integrated together seamlessly.
Now about the market share, well take note that LR is available on both platform so it is likely Adobe will put in the Windows users (which will be A LOT) in it too.
Now, I hope the faces thing makes it into Aperture, I know some doesn't like it, but I think its kinda useful for some purposes. And an easier way to upload to flickr or facebook will be appreciated. But the most important thing Im hoping for is real speed boost, low resource hog, makes use of Open CL and GCD and non-destructive plugins (they could implement it like PS layers, that would be sweet, easy to disable and enable the plugin effect and even stack em up or delete the previous ones), also improvements in the adjustment panels
Go Aperture X!!! (alright the name is weird, for now...go Aperture 3!!!!)
edit: and 64 bit will be awesome!