In his first hands-on with OS X Yosemite, Jason Snell points out an issue with the redesigned title bars that no longer show a title:

I have to admit I’m also a little nonplussed about the disappearance of titles from the top of many windows. In apps that never really have more than one important window (Calendar and Maps come to mind), the title is unnecessary; labeling my Calendar window with the word Calendar seems pointless. But in many other contexts, the title of the window imparts important information, and there’s a danger that some of that information could be lost if Apple takes this approach too far. It’s something worth keeping an eye on, especially given the radical changes Yosemite has in store for Safari.

I’ve been trying the first Yosemite beta on my MacBook Air, and I find it annoying that Safari doesn’t show the title of a webpage (just the domain in the address bar) when a single tab is open. It’ll be interesting to see if third-party apps will switch to this integrated toolbar approach with no separate area for a title.