One thing along this line that has come up is a warning not to use Mirror lockup and leave it open for any extended period of time, especially with a telephoto lens -- the sun can do more damage to the shutter that it would to the mirror/viewfinder.
Now I did one time have mirror lockup engaged for longer than I should of when shooting a sunset. I got distracted by something and forgot to finish the shot and then I heard the snap of the shutter automatically closing (I believe it does that after 30 seconds).
Now it would be fun to describe how I had to wave away a bunch of smoke and yank off my lens and stare at a totally destroyed shutter, but sorry, it didn't happen!
I have heard scary stories about how using a Better Beamer flaxh extender, which has a "fresnel" lens at the end of the extension to concentrate the effect of a flash for a telephoto lens, well, I've heard of camers left with them pointing at the sun, and the results on the flash head were not pretty!