I've been learning about Active Directory Federation for Office 365's Hosted Exchange. Here are some links and notes about the process that I don't want to forget.
Where to sign-up: Exchange Online account ($4/month/mailbox).
Instructions on how to configure DirSync to sync a single OU.
The excellent tutorial that I followed to setup AD FS w/ O365.
A discussion of the 3 sign-in models for Office 365.
A discussion of whether to use SQL or WID for ADFS authentication to O365.
Should you use O365? Yes!
How to test AD FS functionality: https://adfs.trimideas.com/adfs/ls/idpinitiatedsignon.htm
Introduction to Azure multi-factor authentication for Office 365 (it's free!).
The AD FS Proxy appears to fetch configuration information from the AD FS farm once per minute.
This guy says the Web Application Proxy can route requests to different servers via hostname!
Here's how to configure extranet lockout with AD FS 3.0. You can only configure this on the primary ADFS server...and I think it pushes the configuration out to the web proxy, but haven't validated that thought.
Here's how to customize the logo on the AD FS sign-in page.