True but an even greater upgrade is linux (im talking about general running, not program compatibility)
mainly because it doesn't sit there and eat up an inordinate amount of memory just sitting idle

Anyway back to the topic, yes we must unfortunately as sadly a high amount of users are still using it, this causes the problem of having to have CSS hacks all over the place but also it means that new technologies will take even longer to become main stream.
Personally we should, but from a business perspective you really cant afford the drop in visitors to your site.

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mysql> SELECT * FROM `users` WHERE `users`.`clue` > 0;
Empty set (0.00 sec)