I like something other than plain black...the trick is implementing it correctly (as in aesthetically pleasing, lined up, centered, or whatever OCD quirk you may feel when you as the mapmaker look at it). If you find a background that you like and you fit it properly, I'd be happy to put it up. But it's totally your call.
When scrolling around huge maps, it's easy to get "lost" in large expanses of black (or a solid colour), so there's a utilitarian purpose for having something else there.