Damn. Like a faithful MacHead, I popped into my local Apple dealer - which luckily really is local - and picked up a copy of iLife '05. Having "Camera RAW" format usable in iPhoto was enough of a useful feature to get me to part with my CAD$99.
Sadly, it's not a bed of roses. People who already use RAW normally also use Photoshop - and even if iPhoto 4 couldn't view or edit a NEF, it could launch Photoshop which would. There are two problems with this picture in iPhoto 5. Firstly, Apple accidentally disabled the "Edit in external editor" contextual menu item. Once you work around that, you're in for another shock - when your photo opens in Photoshop, it's as a bloody JPEG!
In fact, it looks like the way iPhoto deals with RAW files is by converting them to JPEGs before doing anything with them. The RAW files are still there, you can get at them via export or by dragging out into the editor of your choice (provided you haven't edited in iPhoto - you will have to "Revert To Original" if you have.) This will make some user's lives a bit easier - because everything can handle JPEGs and so a lot of typical workflows will be more straightforward this way. But this still feels a bit half-cooked, and I've noticed a few other little flakinesses that really shouldn't have escaped QA. The "external editor" menu thing is pretty inexcusable IMO.