See this article for more information:
http://www.shacknews.com/onearticle.x/51456

They'd already said more portal was coming.

I'd wait for an official announcement for Portal 2 though, not just some dude on that other site who said he heard it from that Valve Doug whatshisname.

As in the lead designer? This is official enough.

I thought someone said he'd 'heard' it from the lead designer. There's been no official interviews or announcements on it.

It is at least a little bit more information hinting about it though, and more official than before, right?

Well they'd already said in the commentary that they wanted more, but this is good. What we didn't know if it would be expansion style (more maps etc) or a complete sequel.

Also, I'd take the lead designer saying that there will be a sequel is pretty much confirmation. Considering she was hired to make portal, you'd think she would know.