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.