The Pre supports cut, copy, and paste, but I don't think the mechanism for doing this is intuitive, so I've put together a quick guide.
To select text, hold down the Shift key and drag your finger over the text you want. This takes some practice, as the Pre tends to stop selecting text before I get to the end of the word. A hint: Drag way past where you think you think you should have to.
To copy the text you've selected, you can use the drop-down box, but a faster way is to tap and hold on the gesture area* and then hit the C key. To paste, you hold down on the gesture area and hit the V key, while cutting is the same with the X key.
You can use these functions in some applications, but not all. You can't use CCP in the web browser, for example.