I've just spent 5 mins playing with a new iMac...
The new keyboard...ARRGGHH

!! Most importantly, they have crippled Expose. After 4 years of F9, F10, F11 being hard coded into my brain, now I've suddenly got to learn F3, or else press the FN button plus the F9, F10 and F11. I can pretty much do without F10, but no single buton "show the desktop (F11) is a killer for me. I don't currently use a Mighty Mouse, but I think it might take over Expose actions, and I've got some serious re-learning to do. I can see a significant productivity hit coming when I upgrade... Finally, if you forget that things have changed, then you find yourself muting or turning down the audio !!!
I'm just hoping that Leopard has some sort of panel in System Prefs that allows you to set your keyboard back to the old style, with the function keys not needing FN to be pressed, and the ability to assign the multimedia controls (audio levels and eject) to the F16-F19 keys above the num pad.
Why would Apple decide that we all need to learn a new set of keys for things that have become instinctive to so many seasoned users

. And why turn elegant single keystroke tasks (tile app windows, show desktop) into ungainly two simultaneous key actions, with the FN key located somewhere that you hand rarely goes ! When the hands in the standard typing position (fingers on ASDF.... HJKL and thumbs on the space bar), getting up to FN and pressing F11 is hella awkward...
http://images.apple.com/imac/images/gallery/keyboard_3_20070807.jpg
I'm not that excited about the tactile feel of the new keyboard, but that might just be a 'getting used to it' thing. However, something tells me that the price of the old style wireless keyboards on the second hand market (those with the full num pad and old school keys) just got a lot higher.
Other observations....
-glossy screen does have more reflections, but your brain ignores them pretty quickly. Not so sure about the eye health / brain strain issues with this though, however I suppose its no different to an old CRT or a TV
-overall look is quite nice. Definitely not ugly, but neither does it make me think "work of a genius" like previous Apple products