Just noticed a really neat, fairly new (I saw the link a couple days ago, I think) feature on Strava called fly-by. Essentially, it shows your ride and all the people with whom you crossed paths on that ride.
Look in the upper left, and it'll play them like a video, so you can see where other people were while you were riding. And when you do the animation, it'll animate them, as well. I don't know, if you're doing something like a short race, if it'll give enough detail to see jockeying going on in a ride (I suspect not), but it's still really awesome.
I'd also call it evil, in terms of time-wasting potential.
But it's fantastic, too, if you meet someone on the road or trail, and can't remember their name (or how to spell it). Now you can just watch your ride, and look for the intersection or overlap. Sheer genius.
Disappointed that this now means I know that the person who passed me this morning is not on Strava (well, or hasn't uploaded their ride yet, I guess). Was curious.