that's a good site, but if a website is hosted on a different server in different areas, it'll show as up for someone and down for someone else.
Example:
http://nanowrimo.org <- it's hosted by Amazon EC2 volumes, and my area falls under the N. Virgina one. Same for my Netflix online streaming. Can't get that on my tv. :( Been down for 18 or so hours.
http://status.aws.amazon.com/