I've been using Verisign's Managed DNS for about 18 months now. They offer 100% uptime not just 99.999% but 100%, "Reliability with 100% DNS Uptime Service Level Agreement." Well their DNS went down for over 155 minutes on 7/31/2003. So much for 100% uptime.
http://www.verisign-mdns.com
What gets me about this is that they have 4 servers located around the world and all 4 went out at the same time. When I signed up with them, I figured that if all 4 servers went out it's World War III. When I found out that they were down I had to turn on Foxnews to see if something was going on.
Just goes to show, you can't trust ANYONE with your livelyhood.