The demo I saw was around the standard Collaboration Portal of SharePoint.
Thoughts, from a look and feel issue the improvements are simply evolutionary and not that impressive. One thing now is you can type text anywhere in a area, getting ride of the need to but content web parts to place plain text and graphics. I have always seen the content web part as the key part of making a SharePoint site work and it was nice to see that you can now add text, like instructions, everywhere.
BUT, overall there was NOTHING new for the UI of this Portal. There was a button marked feedback that I was desperate to touch but we were all there for accessibility. The talk was about SharePoint 2010 accepting Accessible Rich Internet Applications ARIA. ARIA tags can make reader devices more aware of the roles of items on a page. So if you use them right it will mean things like JAWS will have an easier time reading SharePoint.
Accessibility with current SharePoint is awful and this could be an improvement, but we didn't actually see SharePoint 2010 run with JAWS so lets not celebrate yet.
Microsoft is also talking about being closer to WCAG 2.0 and XHTML. But it is important to state that they goal is "closer to" rather than "fully compliant." I would go to say you probably could not make the HTML that SharePoint 2007 creates LESS XHTML compliant if you wanted to, so this may be no big thing.
Looking at the standard Portal SharePoint 2010 did not look very impressive. But the "feedback" button has stuck in my imagination. I gather that there are some wonderful new social networking tools added to extend beyond MySites. As of yet I have not gotten a chance to see them.
Also the cries for online Sandboxes is clearly becoming a scream to Microsoft. Please if you blog or Twitter just keep up the pressure on Microsoft. The rep who I saw seemed to not even understand that the beta was beyond almost all of our machines. I fear that SharePoint has been taken over by marketing people who don't really understand the issues involved with 64 bit and they will need to be educated by the user population that we need support in accessing SharePoint from machines with 32 bit OS. It was good to hear that my issue was part of a choir of users and hopefully Microsoft will get the point soon enough.
But all in all, 2010 is an evolutionary step not involving radical change but also not offering vastly improved UI. You can probably start designing your projects for 2010 now as long as you have 64 bit server architecture. But you are not going to get the wow factor MOSS 2007 produced. 2010 looks like an improved MOSS 2007.
On the other hand it was not a bloated mess, so I am starting to think we are not looking at SharePoint Vista here.