We've made a couple of big changes with how buttons work in 2.5. First of all, we've moved the buttons outside of the dialogs. In previous versions of the software, dialogs that didn't fit completely on the screen had scroll bars. This worked well except for the fact that users would have to scroll to the bottom of the dialogs to click the action buttons like "save" or "cancel".
All of the action buttons in the software now are displayed at the bottom of the dialog, outside the scrollable area. This makes it much easier to quickly select an action.
Another big change that we've made is adding color designations to dialog action buttons. Buttons in dialogs are now colored to make dialog interactions more intuitive. Dark blue is used to designate the primary action. This makes it easier for the user to choose the default option so they don't have to think as much about each of the choices.
Similarly, actions that are potentially destructive are colored red. This subtly warns the user to be sure of their choice.