Yammer is Twitter for corporations, but people don't need or want corporate control over their twittering.
"Anyone with a corporate email can sign up and follow other people in their company. But if a company wants to claim its users, and gain administrative control over them, they will have to pay. Its a brilliant business model."
I don't know about you, but I don't exactly want a corporate IT department controling my communication apps. Plus, doesn't this sort of sound like racketeering? It's not like Get Satisfaction, where companies may pay one day to participate and get data. No, companies will pay to "gain administrative control"... ie shut it down/make it no fun, kill the community. If I'm placing my bets, I'd lean towards companies becoming more open and participatory, teaching employees how to behave in public and seeing the ROI from that involvement, not locking them up more.
Didn't we try this with instant messaging, and didn't IT departments just concede victory to AIM and let everyone put AIM on their desktop? Sure, it came with that silly disclaimer IM, but people wanted the same apps they used at home to be available at work. Add on the fact that Twitter is on mobile via SMS and will soon go live again on IM, and there's simply no way companies can block usage.
Companies may in fact wind up signing up for this, but I can't imagine that many employees would really want to us it.
Big corporate, please keep your filthy hands off my 140 characters!