So today people at Yahoo are playing with Yammer — the ‘Twitter clone for business groups’ that won the TechCrunch50 yesterday.

It seems somewhat useful, in that it’s stimulating discussion between people in the company who wouldn’t normally interact, but by the same note, it’s a third party service so no-one should be trusting them to keep confidential information safe.

Something that comes to mind, though, how does Yammer handle removing individuals who leave a company? It seems that once you’re signed up, you’re in the network. Even after you lose the yahoo-inc email address, it just serves as an identifier and so long as you don’t forget the password, you can continue to participate and read the internal discussions of your co-workers. Surely some sort of weekly ‘Click Here to Remain a Network Member’ confirmation email is required, to ensure that people don’t linger around.

You can have admins, but that’s where their business model kicks in. It costs $1 per user per month to have admin functionality for a company. So within companies just using it for free, there’s no options for that sort of thing.

I can’t decide if it’s cool yet. It’s neat, and people are giving it a good try so we’ll see if it sticks. They’ve done well to produce a good suite of features for launch (XMPP, desktop app, BlackBerry app, reply tracking, tags integration), so it’s in pretty good shape. For Y! we hit an issue of sharing corporate secrets with a third party, so there’s a limit to what people will talk about on there (or at least, there should be a limit…). We really need a Twitter clone running behind the firewall for that sort of thing, but building it, as well as the API and supporting applications is difficult to justify.