The more I use Obsidian Portal, the more potential I see in it.
I'm using it for my L5R game that (finally) got started last weekend, and we're going to have a sizable gap between sessions, because July isn't looking so good (sorry, guys). And August is 100% up in the air.
I have a notoriously bad memory, but Obsidian Portal lets me hide pages (or parts of pages) from the players. And what I'm choosing to hide is reminders and suggestions.
For example, Session One has the events from this session. And the players can comment and add more info (and add poetry, because even bad poetry is usually a good thing). But if you scroll down, there's something you won't see, there. And neither will my players. Because every single page on Obsidian Portal has a "GM Only" section which only that game's GM (or GMs) can see. So I've been stashing notes for the next session in there - planned events, characters I hope to introduce, and so on.
Most pages also have a "Player Secret" section, where I can choose players and allow them (and only them) to see that secret. In fact, I can use multiple Player Secret sections and share different secrets (or disinformation) in each one. It's really cool. Players also have the ability to add secrets - and they can decide who (other than themselves) can see these secrets.
There are games where player secrets are more important than others. This isn't one of them - but I can see this sort of thing working really well for a Paranoia game. Or some espionage-themed games. Or games where the PCs are rivals as well as a team (Smallville springs immediately to mind as a possibility for this ... ).