So 37signals is reporting on Apple's decision to drop support for IE 6 in MobileMe. I'm sure there are many who would like to drop IE 6 from a great height. I will confess that in my current position as a web developer for a NZ bank, I have users connecting with IE 4 and NN 4 browsers. This is a situation I inherited and one I'm happy to relinquish when my notice period finishes in a couple of weeks time. One of the major issues is that there is no way to correlate the user with the browser. This means there is no way to contact users of older browsers and assist them to upgrade and as a result the bank's sites are all lowest-common-denominator HTML. Of course to get into this situation in the first place required a hefty portion of mediocrity which included very little cross-browser testing. The average user experience is likely be fairly average but only the user knows.
Which brings me to my prior position, also for a NZ financial organisation, where we did take a lot of care with the sites we published. There we also had users connecting with older browsers but we kept a record of which browsers a user connected with. As usage of older browsers dropped away we found we were able to contact the typically small (<100) number of users affected and arrange an upgrade. Feedback was generally really good, some folk were happy to have an excuse to upgrade, some folk had access to a supported browser at work (and sadly one old chap conveniently popped his clogs).
I can appreciate that Apple wants to have absolute control of the user interface design and requiring a modern browser must make that easier. I had a quick look at the page info for MobileMe, there's a lot of stuff coming down the pipe to your browser, far more than I would allow for my web applications — most of my users are still on dial-up and the user experience would be dreadful.