The new keyboards feel exactly the same as the macbook keyboards - maybe even more sturdy (less mushy...if that makes sense).
Layout-wise, if you have or have seen the new Santa Rosa Macbook keyboards, it's the same as that. It has things like expose, dashboard, and play/pause/volume options mapped to the function keys with little icons printed on the keys, representing each function.
As far as wired vs. wireless, I can't recommend the wired one enough. Battery life may be better on a wireless keyboard vs. the bluetooth mighty mouse, but I wouldn't risk it. My bluetooth mighty mouse eats batteries so fast that I'm tempted to "downgrade".
The wired one also features a number pad (wireless one doesn't) as stated, and the wireless one might also be missing USB ports (or at least the old clear/white-styled apple wireless keyboard was missing them) - for reference the wired one has two USB ports on the side and comes with a USB extension cable to plug into the back of an iMac, for example, if you needed quick access to a high-powered USB slot without having to turn your computer around (in your case it'll probably just be something you'll leave in the box).
My personal opinion of the keyboard is that it is AWESOME. It's a HUGE improvement over the old one and if you're already used to laptop keyboards, then you'll definitely love it.