I migrated my MacBook to a new MacBook Pro 2010 release using Migration Assistant and just as many others, found that my iPhoto did not show any photos (only thumbnails) as well as iTunes did not show any music. The Finder did show the files though.
And don’t blame Migration Assistant for it. What has happened is that you are probably running older versions of iTunes and iPhoto (and probably OS X too for that matter) than you were at the other Mac. So, just run Software Upgrade (with restarts and everything) until it tells you that you are up to date. Then all should be well with iTunes and iPhoto too.
Credit: this tip was kindly pointed out by AndyField. Thanks!