Les Mikesell:
Things really have to go out of their way to break the basic X mechanism of highlight/middle-mouse to snarf and barf. Unfortunately, a few things do
Tim:
Pan and Evolution are two things that come to mind.
Les Mikesell:
What doesn't work as expected in evolution?
Frequently, when trying to middle-mouse paste something that you've highlighted, nothing gets pasted. Particularly when trying to work between two Evolution windows (e.g. an editor as well as the reader).
Pan just won't do it, at all.