A bunch of answers:
Steve and LookingForSolutions - no, RU6 is the only delivery vehicle for the security fixes shipping tomorrow. We do have a fix in process for the RU5 SCR issue but we didn't rush to get it into RU6 because we did not hear a lot of outcry that this was a big problem. In the future, please let us know at the forums at http://social.technet.microsoft.com/Forums/en-US/exchangesoftwareupdate/threads/ because my team actively investigates and tracks issues that are reported to us there. (We also listen to CSS and the reported cases there, but sometimes it takes longer to get through that pipeline). We're also working on a workaround that we'll post here tomorrow.
Johannes - yes, but we can't talk about any formal plans or dates until April-ish
Cameron - we have the same hopes. <g> Honestly, my team did not get a lot of negative feedback from RU5. I know about the SCR issue that Steve mentioned above, but aside from that, I'm not aware of any particular issues.
Robert - to install an Update Rollup, you need to have the same level of perms that you would need to install the Exchange software itself
mwa - This rollup is smaller than our typical one but does have a handful of fixes and CDCRs. We wanted to minimize the number of non-security fixes because we all know that more churn means more risk. We're just trying to find the right balance, as pushing out fixes to later rollups means people wait longer for fixes that are important to them.
Mike - your CSS engineer that gave you the interim update can provide you offline with a list of fixes that will be in this rollup to help you determine whether or not your fix is there or you need a new interim update. And I hear you on the process - we're looking at ways to automate it. Stay tuned.