Good info here at the USGS.
Apparently, it happen at 5:25 am PST, and I had no idea. About 1 in 4 or 5 people I spoke with today either felt it, or were woken up enough to realize something had happened, but weren’t quite sure what.
Here’s a good map at the USGS site which measures how many people responded and intensity.
The vibrations and earth movement could be felt for only a few seconds, though it happened along the Nisqually fault, where the February 21, 2001 6.8 earthquake occured.
Map of that quake’s intensity here.