Digg vs. Reddit
Now here's something interesting. You can imagine two competing products to have the same user-base if plotting both in a graph draws a symmetrical pattern: where the rise of one is the fall of the other. Digg and Reddit offer social news services. Digg got in to a lot of trouble in 2010 since they released version 4, criticized by Reddit's Alexis Ohanian to be a victim of VC meddling that departed Digg from its core.