I really need something like this, and I think they've nailed the UX... but it appears to use GoDaddy to do the whois. I don't have any personal experience but a quick google search will back me up when I assert they are notorious for not being trustworthy with your whois queries. A site like this that I felt like I could trust would be a daily destination for me.
It's way too fast for whois. They're probably using the COM/NET/ORG Zone files in a nicely indexed db. I'd be interested to know more about the back end - they get points for responsiveness.
