When Screen Sharing, why does the remote screen continually go black?
I'd second the idea that it may be a RAM issue -- I'm noticing that it happens particularly when:


I've got huge uptime on the remote system (so... memory leaks, cruft, have accumulated)
I switch apps on the remote system (loading things in and out of RAM)


From practical standpoint, I've found that greping for the the screen sharing daemon and killing it forces the remote machine to respawn a new one that isn't blacked out... but that doesn't last for long:

ps aux | grep screensharingd

and then sudo kill XXXX once I know what what procid I'm targeting. But that's a really short term solution (buys another 15-90 seconds, usually).

The finger the I would also point is at mdutil, the spotlight indexer, which just gets out of control, especially on a system with a lot of large drives with a lot of small files. I've had best success clamping down on Spotlight (which, imho, isn't very useful) and restricting it by either marking most of my drives and directories "private".

If the remote system is tight on RAM, it may be because Spotlight is being a pig.