I’ve had this question asked of myself quite a few times now, and my response has been sure – as long as the application providers you run on your server support it. By that I mean things like your AV vendor and any LOB software that you run on the server need to support the Service Pack 1 for Windows Server 2008 R2. I know that Trend as of WFBS 7.0 Build 1435 support it and now the SBS team have come out to say that yes – the in fact recommend it here
What about SBS 2011 Essentials I hear you ask? Well if you look carefully you will see that SBS 2011 Essentials already has Service Pack 1 installed as it came out a few months after the SBS 2011 Standard edition.
Ok – what are you waiting for… do your backup and get on with it.