IE 6 is a last-generation browser. This means that IE 6 can’t provide the same web experience that modern browsers can. Continued support of IE 6 means that we can’t optimize our interfaces or provide an enhanced customer experience in our apps. Supporting IE 6 means slower progress, less progress, and, in some places, no progress. We want to make sure the experience is the best it can be for the vast majority of our customers, and continuing to support IE 6 holds us back.
37signals Product Blog: Phasing out support for IE 6 across all 37signals products on August 15, 2008