Exchange

Lots of places have announced it and I might as well too.

One of the biggest feature points for me is Windows 2008 support.
You can download Exchange 2007 SP1 here.

Some noteworthy changes:
New Client Access Features in Exchange 2007 SP1
New Transport Features in Exchange 2007 SP1
New Mailbox Features in Exchange 2007 SP1
New High Availability Features in Exchange 2007 SP1
New Unified Messaging Features in Exchange 2007 SP1

There are some very 'techie' ESE changes in SP1 which could help prevent data loss from potential B-tree bitrot corner cases. Very cool changes in my book!

Service Pack 1 for Forefront for Exchange also came out within hours of Exchange 2007 SP1.
You can check out the changes here.

This problem can occur with more than just Exchange 2007. It can happen with anything that is .NET Framework based. The root cause typically is due to a proxy misconfiguration or if HTTP traffic in general on your Exchange server is severely limited.

To workaround the problem, check out KB 944752.