This may have snuck by a whole bunch of folks, so I thought I'd write a quick post about it. First off, sp3 isn't out yet, but it's currently in progress.
exchange 2007 owners can expect another service pack, specifically SP3 is scheduled for release in the later half of 2010 to add support to Writable windows 2008 R2 domain controllers as well as installing on Windows 2008 R2 servers.
Kevin Allison's original post on the Exchange team blog on this may be found here. Reading between the lines there's a ton of good stuff that's happening behind the scenes that we may still benefit from in the exchange 2007-2010 upgrade experience – we live in hope of one day being able to do an in place upgrade without deploying new hardware side by side.
And finally, since this is a service pack, were hoping for even more functionality to sneak in while were not looking 😉
Definitely Sp3 is a space to keep on watching.