I was reading this old series of posts on the whole Office Ribbon bar design (quite a fascinating from a developer perspective). I came across the comments where quite a few have ranted on the 'paste unformatted text' as being more preferred than paste. I too used to be in that same group but that was before I came across this whole section dedicated to configuring copy-paste under the Advanced tab in Word options. Here you can configure the default paste action. For keyboard freaks there's always the Alt+H, V, S to get to the Paste dialog.
While we're on the topic of Copy/Paste. Do yourself a favor and install ClipX, you have absolutely no idea what your missing.