Internally at Microsoft, we have had these things called "Exchange Technical Bulletins" that were organized by Nino Bilic.  These nuggets of information were very useful and I have gone back to them many times to look for things that I had forgotten.  For us they worked well, but they weren't available to our customers because they really just weren't "customer-ready".  Now, they are being ported over to a customer friendly format and will be available publicly.

http://www.microsoft.com/technet/prodtechnol/exchange/2003/insider/default.mspx

Keep checking for updates since there is a lot of content that still has to be converted...  There isn't an RSS feed on the page yet.