From the Harris Cyclery website:
Dear Harris Cyclery friends and customers,
It is with heavy hearts that we convey to you the news that Sheldon Brown has passed away. Our thoughts go out to his family at this time. The cycling community has lost one of it's most passionate members.
Word is that Sheldon suffered a massive heart attack after enduring four years of a debilitating rare form of MS. Sheldon Brown's pages, which I link to below and at right, are both an inspiration and an absolutely priceless resources for the do-it-yourself bicycle enthusiast and for anyone interested in bicycles. Browsing through his massive site, you can also learn about almost every aspect of the man, from his eclectic passions and his wonderful family, to how to adjust your Sturmey-Archer hub. I never met him, but looking through his site makes me feel like I did, and my best wishes go out to his friends and family. Ride in Peace, Sheldon.