This is possibly a Delta launch, and not a Shuttle launch. Either way, very cool. Thanks to commenter Paolo below.
BABloggee Greg Smith pointed me toward this amateur video showing a Space Shuttle launch from an airplane window (note: mild NSFW language in the vid)!
I have to say, this looks real to me. Hard to say if it's a Shuttle or some other rocket, but the footage itself appears legit. Normally NASA restricts the airspace around a launch, but judging from the video it looks like the airplane was 50 or more miles away from the launch site. The rocket veers away from the camera, indicating the plane was west of the launch, so that hangs together as well. Sadly, the video ends before the solid rocket boosters separate from the Shuttle (which happens roughly two minutes into the flight); that would be very telling, and I have to admit it's weird the video doesn't go for longer. The problem with videos like this is the lack of any real info on the hosting sites! If anyone finds more, please leave a note in the comments below.
I have seen some weird stuff from airplanes, and I carry my camera on board all the time now Just In Case. I'd dearly love to catch something like this...