I absolutely love the wireless one.
It's got the perfect size: no number pad takes away space or get's in the way. I can type on this thing much faster than on the old keyboard, and it feels much less clunky. It's really the best keyboard I have ever bought and I literally take it to bed with me sometimes (no... as the best remote control for EyeTV and Front Row I have ever had, that is

). That's were the lower weight compared to the old one and the smaller size without the number pad come especially handy. However, let me say, that I have a wired keyboard lying around on my desk, which I occasionally use for calculations with the number. And of course, I have grown up with notebooks - my first computer was a notebook with notebook keys.
The wireless keyboard is not perfect for everyone. So I really understand and do have some sympathy for people who like the old white plastic one better - be it for the number pad or for the key drop, or something. But these people can surely some keyboards from 3rd party vendors (like Matias), which should even feel and work better than the old Apple one. Face it: the old wasn't the most ergonomic keyboard or the one with the best feel to it. And if you have disassembled one, you know it's pretty darn cheaply made.
(PS: There is one small caveat however: When both the wired old one and the wireless new one are connected, the function keys for Exposé, Dashboardm, Display brightness etc. are not synchronized. They are on different "F" keys. Which is a bit annoying as I haven't yet found a way around that. But as I use the wireless one more and more, it's not that much of a problem anymore).