You are likely to want to do things to the text that you just yanks / pasted (wrap it in brackets etc).
Is there a way to know what you just yanked? If so I would quite like select it (put the mark at its beginning and the point at it's end).
The obvious things that come to mind are advice for the yank functions.... but I'm hoping that there are some magic variables for this.
(region-beginning)
and(region-end)
give you the yanked region after a yank.