Excellent tip, thanks Paul. Sometimes I run into the same problem with Safari 3, even though I can change its user agent. It's ridiculous and the real problem lies with the site designer, or should I say, the person instructing the site designer to impose this limitation.
Even more annoying are websites that fully depend upon Flash to be able to use them, but thankfully I don't come across them as often as I used to.
Next time: How to convince more site designers to work with proper webstandards, not just IE6. Or even: How to convince more websites to work with ArcWeb.