Ah, that's a nice thing. Back when I used a mouse most of the time (back when I mostly used a desktop rather than laptop), I really liked middle mouse button paste in X, as merely selecting text wouldn't overwrite the clipboard. I used it all the time and it was probably the biggest single thing I missed when I had to use Windows or Mac. It's super handy, IMHO.

For non-X users who have no idea what I'm talking about: In the traditional mouse button setup for X Window System, you can select text, and then paste it by clicking the middle mouse button.

I don't know if I can train my hands to be able to select/drag with a trackpad quickly...just trying it now seems very clumsy and time-consuming. But, I do often wish for the ability to copy without overwriting the clipboard.