I've noticed a drastic decrease in online activity the last few days.  I've also had much more trouble with ICO.

Specifically:

It takes a long to post a line of text.  That is, I type in the chat something like "hello" and 30 or more seconds later it appears in the chat.

I've also had more problems with "Disconnected from ICO." occuring in good games after an hour or two.

Other online games work fine, so it must be something specific to Sins and ICO.

Surely the decreased player count is evidence that this is more than a few players.