I dunno if it's a blessing or a curse, but lately I've been cropping a lot of my photos to fit the Facebook cover photo area on my profile (851x315px if you are curious). It's actually not a terrible aspect ratio for panoramas. Anyways, here is my latest cover shot.
Incidentally, if anyone else is frustrated by facebook's terrible jpeg compression on cover photos, I finally found a half decent solution to the problem. All you need to do is export your photo at exactly 851 by 315 pixels and then make sure the jpeg image quality is set such that the image is less than 100K. That way Facebook won't re-compress it at all. It might not look amazing out of your computer, but it is sure to look better out of lightroom or photoshop than out of facebook's picture mashing machines.
Incidentally, if anyone else is frustrated by facebook's terrible jpeg compression on cover photos, I finally found a half decent solution to the problem. All you need to do is export your photo at exactly 851 by 315 pixels and then make sure the jpeg image quality is set such that the image is less than 100K. That way Facebook won't re-compress it at all. It might not look amazing out of your computer, but it is sure to look better out of lightroom or photoshop than out of facebook's picture mashing machines.