Not quite. IE8 is making huge gains in market share, but almost entirely at the expense of IE6 and IE7. The overall IE marketshare is holding somewhat steady at 60%. I think what you're seeing is Windows users are perfectly happy to take an upgrade that Microsoft offers, but either afraid to branch out to a non-MS browser or else just don't know how to do so. Windows 7 shipping with IE8 has a lot to do with it, too, as people buy new laptops, etc, and never touch the browser it comes with.
Reference: http://www.eweek.com/c/a/Windows/Microsoft-IE-6-Share-Falls-...
I wish Chrome would take more from IE than it is from FF, but it is good to see IE6 drop so much. It's under 5% now.
Note: these are US numbers. If I recall correctly, the global numbers are shaded a little more non-IE.