Web Browser Compatability

When doing a website, do you think it's right to be code for only certain browser (ie the most used browsers like Firefox & IE (latest ver)) and to just say to other users of browsers like Safari, IE 5 , "sorry you cant use this site"

ACID3? Is bullshit. It tests things like DOM2 and CSS3 that aren't even completed standards yet, so if you develop a website that uses these features, you fail.