I love our Pingdom account it’s great for monitoring performance and notifying of you if there are server problems.
This is an interesting graphic from Pingdom our response times have dropped in half since Jan 27, 2010 . There could be many contributing factors network activity, server load etc for this.
I think the real reason was we dropped some mu plugins on that date:
WPMU-Topposts was a total hog. I noticed a drop in CPU use immediately upon removing. It was basically writing to the db every time a page was opened and sorting several million records to determine which blog was popular, a cool feature on the homepage to show the most popular blogs but who cares if it is making the server sluggish…
Or it could have been a magical network change, who knows as long as the curve is not going up that quickly I am happy.