The SharePoint Conference 2009 is a bit of a misnomer, since it's almost all about the forthcoming SharePoint 2010 edition. Microsoft should be commended for the depth of the program, though at this early stage, many sessions still leave you asking more questions.
We will have a lot to say about SP2010 (critical analysis that we'll share with our SharePoint research subscribers) but in the meantime, I'll make one broad observation about the user interface: it has become more of a power-user platform. Microsoft talks a lot about "empowering the business", but a lot of what I see is really about empowering the administrator or site manager.
Power-user features (like changing page and site configs) are very welcome in any tool, but in software power always equals complexity. Even for the everyday knowledge worker, it seems to me that there is a lot to grasp and master in this interface once you get beyond tried-and-true file sharing.
To be fair, the user experience does change from module to module within SP2010. Microsoft also argues that its famous "ribbon" will acclimate users, and I tend to agree (though not everyone here does). But this brings up another issue: the UI is starting to get a bit cluttered. One of the useful things about viewing demos at conferences is that the presenter has to downsize their screen resolution to more plebeian dimensions, and one of the first things I noticed was that for some scenarios, SharePoint wants to occupy an awful lot of vertical real estate.
Contrast this approach with the efforts of Google and others to try to streamline user interfaces to the bare necessities. (Kas has some good observations here.) Of course, Microsoft has a bigger challenge, because they want SharePoint to do, well, everything.
Just don't assume that this UI is going to be plug and play within your enterprises. Your SharePoint team may come back from this conference rightfully jazzed about all the new capabilities, but don't underestimate the training required to exploit them properly.
And then, don't underestimate the governance required to keep your SharePoint sites usable on an ongoing basis. In some of the demos I saw, the accumulation of web parts started to make collaboration sites look like MySpace pages. Even more so than 2007, SP2010 will punish enterprises who let end-users run amok.