Cut/Copy/Paste in Quicktime X

"QuickTime Player X does not have many of the more useful editing features that was available in QuickTime Player 7. You can find QuickTime Player 7 in your Utilities folder if it was installed when you upgraded to Snow Leopard.

Of note, QuickTime X is a new beast that contains QuickTime 7. The Players are completely separate entities from (but use) the QuickTime framework."

"You can use Edit > Split Clip CMDY to cut a video at the playhead.

You can use this as an alternative to Trim. Use Split Clip then delete either the left or right clip. It's much easier to choose a specific frame using Split Clip keyboard controls rather than draggable Trim controls.

How can you delete a span of video from the middle of a clip

Split the clip twice. Then delete the middle segment you've created.

or paste that to another part of a clip?

Use Edit > Insert Clip After Selection... to insert a new clip.

After you have used Split Clip, select one of the resulting clips. It will be highlighted in Yellow. You can drag to rearrange the clips, or press delete to cut the clip out of the video."