For various reasons, some web designers have an annoying tendency to create sites that only work in Microsoft InternetExplorer. Often they've used a Microsoft tool that creates dirty HTML, and sometimes the designers claim that they're using advanced features 'only supported by IE' or that it's 'too hard' to design and test for more than one browser.
There are a number of sites that discuss this issue.
HallOfShame?
There are a number of sites in New Zealand that suffer from this problem. Feel free to add any you encounter to this list:
One page links to BrowserSpecificSites: