Did you have issues using a Microsoft 4000 keyboard with your Mac? When I had a iMac (about 3 years ago), I tried connecting my Microsoft 4000 keyboard to it and I remember that there were some issues with key mappings.

I do like Mac keyboards, but at times I like the more relaxing feel of my 4000.

Is it possible to make the keys match 1:1 so there is no difference between which keys I press for each keyboard?
The only issues I had (on Lion) were with the Microsoft drivers not retaining their settings between reboots. It seems the drivers were vastly improved (no more kernel panics) since you've tried them; see David Röthlisberger's article.

Other than that, I think the ergonomic part is well worth the trouble of getting the 4000 set-up properly. And with KeyRemap4Macbook you can get almost limitless customizability.