Yesterday I downloaded and installed the Yosemite beta. I installed it on a separate drive so I can choose to boot from it or from Mavericks. I'm an Apple geek so I thought I needed to do this. But I'm also careful and know that beta means it's not finished and I could experience issues.
The first thing you will notice is the new look. The system font has changed and the Apple app icons look just like their little iOS siblings.
Spotlight is new and now searches multiple resources, not just your hard drive. For example, if you search for Steve Jobs the top hit is Wikipedia, followed by the book on iTunes and then the movie on iTunes. When I searched for Volkswagen, Spotlight suggested the Volkswagen website first. You can configure Spotlight searches in the System Preferences and choose where Spotlight will search. The only option at the moment for web searches is Bing. Google is not an option at this time.
iCloud Drive is also something that you can test out. It appears in the sidebar of Finder windows just like Applications, Desktop, Documents and Downloads. There are default folders based on applications. There are folders for Automator Scripts, Keynote, Numbers, Pages, Preview and TextEdit documents as well as one labeled Quicktime Player and Script Editor. You can create your own folders as well. You have options for configuring iCloud Drive in the System Preferences. You can choose which apps will store documents and data in iCloud. There is also an option to Look Me Up By Email. This will list apps that allow other people to look you up by your Apple ID. People who look you up will see your first and last name. You can control which apps have access to this information.
Also in the iCloud System Preference settings are the Family Sharing settings. This is where you can setup a shared iTunes account for up to 5 users in a household. In addition to sharing iTunes content you can also set up a family Calendar, share photos and share locations. This looks like it will be a really nice feature and offers more than what the current Home Sharing offers. Apple has a full document on this new feature.
That's about it for now. All of the really cool features shown at WWDC require working with iOS 8 like Continuity. It will also be cool to see the new Photos app and how Family Sharing works.