The ripple effect is a good plot device. But back when I used to post on bttf.com's message board, one theory always bugged me. Everyone always said that when Marty cries over Doc at the end of the first film (after he arrived too late to stop him from being shot) that Doc actually was dead at that point. It was only when he blinked that the ripple effect caught up to him, and the bullet proof vest magically appeared on him.

WHAAAAA?!

That doesn't make any sense, and it has nothing to do with the ripple effect as portrayed in the movies! In all other instances, rippling only occurs to things that are already out of their proper place in time. The matchbook from 1985-A that Marty took with him to 1955 ripples to the matchbook from the good 1985. The ripple effect occurs to people and objects that exist separately from the timeline, changing objects, preserving (or occasionally obfuscating) memories of time travelers, etc.

Doc's bulletproof vest has nothing to do with that! While Marty (and the audience) skipped to the future instantly, the timeline had 30 years of naturally-occurring time to realign itself, wherein actual events occurred. Doc read the letter, bought a bullet-proof vest, put it on, pretended to die. It didn't need to catch up with Marty. Marty was catching up with it! Where is the logic in this new timeline magically transforming Doc's corpse into a living Doc?!