I've been doing a lot of iPhoto talks lately, and I've noticed that a lot of people don't know how to preview the images on their memory card using iPhoto 6. I first read about this trick on MacOSXhints, and it's pretty handy.
When you have your camera or card reader connected to your Mac with iPhoto open, hit the Return key twice in succession. iPhoto 6 will allow you to preview the images on your memory card. You can even drag specific pictures to the Source pane.
Once you've finished previewing your pictures, all you have to do is click on the Library folder (or anywhere else really), then back to your Camera Icon in the Source pane, to upload your pictures the normal way.
It's really a handy way to see what's on your memory card before adding the whole enchilada to your iPhoto library.