Update 8/11/08 10:45pm EDT: Gmail is back up now. According to the Gmail blog:
Many of you had trouble accessing Gmail for a couple of hours this afternoon, and we're really sorry. The issue was caused by a temporary outage in our contacts system that was preventing Gmail from loading properly. Everything should be back to normal by the time you read this.
This is becoming an unhappy habit :(
[Thanks to Ed Shaz for alerting me to the problem.]