I, too, have experienced the same "Pages freezing" problem in Lion. I removed iWork '09 entirely and reinstalled from the original DVD. Same problem with Pages. I then tried to restart and was unable to do so because Pages would not quit. A force quit meant losing all of my recent typing, so I decided to do a hard shutdown - holding down the power button on my MacBook Pro until the computer shut down. I had set the shutdown procedure to "Reopen windows when logging back in." When I started up again my Pages document came back in its last iteration; I had lost none of my typing! An inelegant work around, but it worked.
I have been dealing with this exact issue since Mountain Lion. Cut/Copy/Paste + Magic Mouse. Happens with Pages mainly but also sometimes with Keynote, Photoshop, Illustrator and Premier Pro. While I am totally annoyed that there is no fix for this bug so far I do feel slightly better knowing that I'm not insane.
Same problems as described by many on my iMac mid 2011 with Magic mouse. Started doing this on Lion. Not solved on Mountain Lion. Only with Pages, Keynote, Numbers.
At least now I know what it is and can stop reinstalling and other trouble shooting. Will try to "retrain myself" with the Magic mouse. I tried Duncan's little test and it causes the bug on cue.
I was planning to talk to AppleCare for months. But it seems that it will just be more of a waste of time. Usually is these days I have found.
Thanks for figuring it out.