Basically, iPhoto '08 and the iPhone don't always play nice -- sometimes, you'll take a bunch of pictures on your iPhone, bring them back to sync up with iPhoto '08, and whoops, iPhoto doesn't see them at all. You can see them on your iPhone, but iPhoto's "Import All" button is greyed out, and they're not showing on your screen (sometimes, I've gotten dotted lines where the pictures are -- I think this all has something to do with a corrupted cache that iPhoto keeps of what's on the iPhone). Fortunately, though it's frustrating, there's an easy fix. Open up Image Capture (you can find it in Spotlight or even Quicksilver if you swing that way) with your iPhone connected, hit the "Devices" menu item, and then "Browse Devices." You'll get a screen just like the one above, with your iPhone's name instead of mine.
Uncheck the "Connected" box, and then recheck it, and boom. Image Capture, and thus iPhoto, will see all of your pictures and happily upload them. Is it voodoo? Sure -- we still don't know why iPhoto loses its place every once in a while (like I said, I'm thinking a corrupted cache somewhere along the line). But it works.