Service Packs typically contain little-to-no features. SharePoint 2013 SP1 is no different, however there are a couple of things I wanted to point out.
First, both Yammer and OneDrive are apparently a critical SharePoint Central Administrator error:
You can now configure Yammer and OneDrive for Business on Office 365 with SharePoint On-Premises integration. This can be done via Central Administration:
OneDrive now replaces SkyDrive in the top link bar. Included with this is Yammer, if you activate the Yammer feature on-premesis via Central Administration.
When you click on the Yammer link, you’ll be directed to /_layouts/15/Yammer.aspx and be asked to log in. That’s about it…
Once Yammer is activated, the SharePoint “newsfeed” will now display this message when you visit your MySite.
For OneDrive for Business on Office 365 integration, again in Central Administration -> Office 365 -> Configure OneDrive and Sites Link, you’ll simply input your OneDrive host in Office 365 (https://<tenant>-my.sharepoint.com) and the top link bar will redirect you there when you click on OneDrive.
That is it for ‘on the surface’ new features!
Another note I wanted to point out is use Russ Max’s installation script. It will save you hours of deployment on Service Pack 1. In addition, a reboot will not necessarily be required.