For evaluation purposes -- to see what it brings to rich web apps -- I've added Internet Explorer 7 beta 2 to the daily browser mix, using it aside Firefox 1.5.0.1 and Opera 8.5 in my daily activities.
It's a competent browser, hosting a number of great improvements, however thus far I've seen nothing about it that makes me believe it will replace my feature-rich Firefox browser, nor does it look like it'll replace the lightweight, ultra-fast Opera browser. It really seems to be more about playing catch-up, bringing some of the functionality that the rest of us have been enjoying to the IE hold-outs.
Will definitely keep an eye on it.