I thought it would be worth mentioning that I've just seen, twice, a kind of slowness in Kile (which is a KDE and therefore Qt-based LaTeX editor) very similar to what has been reported here, now and again, as a slowness in LyX. All of a sudden, and for reasons I don't understand, Kile ground to a near halt, with top showing XOrg consuming 100% or more CPU. (Fortunately, there are four processors!) Closing it and restarting it solved the problem.
Richard
