A couple people replying here have made the point that 'not everybodys browser supports it', which is just your standard chicken and egg scenario involving these sort of things. Like linux and business apps.(We dont use linux b/c no apps. We don't make apps b/c no one uses it). Which is why web designers as a whole need to start saying 'If your using ns4/ie4, for the love of god, upgrade'. I'm willing to bet that probably around 99% people using ns4 that went to some website they wanted to use, such as their bank or something, saw something that said 'please upgrade', with a quick painless link to do so, would upgrade. Most of these people do not form romantic infatuations with their browsers
, and are willing to upgrade if thats whats nesscessary to do what they want to do, but they would not upgrade 'just because'.