Exchange Server TechCenter (redesigned)
The Exchange Content Engineering team (including a couple of characters I've been known to hit the espresso stand with) along with various other folks have released a revamped Exchange TechCenter on microsoft.com as a portal for finding technical information on our software. There's lots of good info up there if you're looking for more help or considering a upgrade or move to Exchange. Also as the Exchange blog was one of the first product blogs at MS there's naturally an RSS feed of recent downloads such as Exchange 2003 SP1 and various KB articles and tools. If you run Exchange and use an aggregator feel free to subscribe.