It's a little thing but a big time saver for me. If you haven't used it yet you should definitely check out the new "Show In Project" function that Aperture 3 has added. It shows up in the right click context menu and the File menu when you are looking at an image anywhere but in the project where it lives.
It saves me so much time that I made a shortcut key for it. Even if I know what project an image belongs to it is so much quicker jumping to that project with "Show In Project" that this is probably becoming one of my favorite new things. The biggest issue is remembering it is there. Just force yourself to use it for a couple of days - even if you don't need it and it will become one of those things you just can't live without. Like when they added two finger scrolling to laptop track pads.
"Show In Project works no matter what you are looking at - smart albums, searches, albums, books. Anywhere that an image shows up except in a project where it lives.