I'm not sure if you can actually access other users' messages and/or game lists. We don't have any report yet of that being possible. And didn't someone report that the bug went away after clicking on "My Account"?
But I agree. As long as the exact nature of the bug has not been determined, it probably _would_ be better to take the server down until this is fixed. Better safe than sorry.
So far, it also seems that this is a cache issue, so users could protect themselves by not using the site until this is fixed (if they aren't using the site, then their info never gets loaded into the cache, and then nobody else can hit it due to the bug).
There was actually an element of sarcasm to my post. I'm of the opposite opinion. At most they just need to switch off their caching and take the increased server load. However I don't see any significant exploit being exposed beyond accidentally seeing someone's shopping cart.
The problem sounds from its description like occassionally the server is deciding that we have a page cached, and don't need to load up from the db. At that point it's giving us the wrong page. The important point there is that it's giving us old information, not anything we can work with. I assume it's not passing a session Id back with the response, so it's almost certainly just a harmless glitch.
If I were GOG though, I'd have called in someone from their bed to look into it.