In Mavericks, how can I make Paste and Match Style the default for Cmd-V?
While it may not work in all applications there is a way of doing this for a large number. Certainly it works in Pages, Numbers and TextEdit but not Microsoft Word, where you have to do it within the application.

All you need to do is open System Preferences > Keyboard > Shortcuts and select App Shortcuts in the left hand pane. Click on All Applications in the right hand pane and the + at the bottom.

In the Menu Title field enter Paste and Match Style then click in the Keyboard Shortcut field and press command-V. Then click on Add

You will now see that your shortcut is added. When you open Pages, for example, you will see that Paste no longer has a shortcut (you could add one using the same method) and right next to Paste and Match Style in the Edit menu is your new working shortcut,command-V. Oh, frabjous joy!