I want my title bars back!
Regarding the iPad-ification of Mac Apps (Reeder, App Store), I don’t think the title bars and toolbars are being merged so much as the title bars are being removed. The close, minimise and zoom buttons are then relocated to the toolbar.
Moving widows around is more tricky without the title bar. One situation is discussed below.
Because vertical space is more limited, I often have windows filling the entire height of the screen; windows are arranged mainly horizontally. With a title bar, the draggable area spans the whole width of the window, so even if only a sliver — any sliver — of the window is visible I can start moving the window without clicking through first. This is not the case with the App Store application. Update: this isn’t very clear. The grab areas above and below the search bar are very narrow so hard to target. Clicking and dragging on the ‘tabs’ (Featured, etc.) does not move the window, or do anything.
But this kind of misses the point, since the App Store isn't really about maximum efficiency and productivity.