I'm sure this has already been said, but my two cents: it depends on your market. I have some sites where 90% of my users are on Macs, so I can do all the latest stuff and not worry at all about IE 6. I have one site in particular that targets people who are not particularly rich or computer savvy, and that one still has double digit IE 6 users, so I can't ignore them. There are a lot more than just IE6, 7, or whatever. Have a look at your options on browsershots.
The question you have to ask yourself is: can you afford to alienate certain groups of users? If so, great.. build a site with the latest techniques. I think our industry has to move forward even if certain Internet users won't. At one time we were having this conversation about Netscape 4. Eventually the cost outweighs the benefit of supporting them, and its not the end of the world anyway.