Here is the blurb from the TechNet download page

Anybody who wants to grab the beta can do so, however, but the usual restrictions apply. To me the most onerous typical restriction is that the machine upon which such a beta gets installed usually has to be wiped and a clean base OS installed against which to apply the final version of the service pack when it becomes available. Thus, this isn’t for production machines by any stretch of the imagination, and I can readily understand why MS wants to discourage home or casual users frm attempting giddy experimentation with this code without fully appreciating what kind of work will be involved when it’s time to replace the beta with the final release.

That said, enterprise and other Windows 7 admins looking to evaluate the impact of SP1 — who usually have test machines at their disposal — will probably want to grab this update and get going on installation and impact analysis. SoftPedia has a pretty nice summary of SP1 available, including a useful overview of the changes that SP1 will bring to both Windows 7 and Windows Server 2008 R2. It’s worth checking out, if you want to understand better what’s under the hood here.