The Exchange Product group does a great job of summarizing the most interesting changes and improvements in Exchange 2010 SP1 in this post
on the MS Exchange Team blog. You can also find a more comprehensive list of the changes and improvements included with this latest service pack in the
"What's New !" section in the Exchange 2010 TechNet documentation.
Exchange 2010 SP1 is not supported any more. If you want to test or deploy in production you should choose Exchange 2010 SP3 version.
The Exchange Server 2010 SP1 (version 14.01.0218.015) has now been released to the public and is available for download
You can find the public announcement from the Exchange product group
It is recommended you download and use
Exchange Server 2010 SP1 Help and
release notes to help you plan, deploy, manage and
upgrade to Exchange 2010 SP1.