Frameworks?

Hi there,

I have a project I'm thinking about undertaking, which in some ways would be similar to LJ. (user profiles, posting content, etc.) I've never worked with any PHP frameworks before, and I'm wondering if anyone has any recommendations pro or con about which I might explore? I reckon that at a minimum I'd need something with database abstraction, user authentication and access modules, session management, that sort of thing. I'm tentatively poking around Zend at the moment, but would welcome any advice or assistance any of you have to offer.

Thanks!

EDIT: Alternately, if you're aware of any open-source-type PHP scripts with LJ-like functionality, a steer would be most helpful! No sense reinventing the wheel if I don't have to...