Today was Ken Jennings' first day as guest host. My thoughts:

I thought he did an outstanding job. I was particularly impressed with his quickness, and ability to transition from clue to clue without missing a beat.

My only minor nit-pick is his voice. This is just a personal opinion because I'm old and don't have the best hearing anymore. The pitch of his voice isn't as easy for me to hear as was Alex's. But all in all, great job!