I've noticed that many of my sites that use CSS positioning don't work in IE5. In fact large portions are off the screen. I know this is down to the broken box model but is it worth fixing it? How many people actually use it? And shouldn't they upgrade?

The site I'm working on now is for a charity organisation so I really want to push accessibility to the forefront. The last thing I want is for them to get calls saying their site is unreadable.

Is May 2007 the time to really give up on worrying about IE5?