Unfortunately there is a contradiction involved between the post, which is bound to cause confusion (as if there is not enough now with the initial bait and switch RU3's).
From here:
"On March 14th we posted an announcement to the EHLO blog about removing Update Rollup 3 for Exchange Server 2010 SP1 due to an issue related to Blackberry devices.
"The Exchange Servicing team has fixed the reported issue with E2010 SP1 RU3"
From the other post, http://blogs.technet.com/b/exchange/archive/2011/03/30/exchange-2007-2010-rollup-3-status-update.aspx
"Specific to this second issue we uncovered a problem which manifested as an email delivery delay for users of Microsoft Outlook 2007 or 2010. Our investigation of the problem exposed a rare situation in Exchange 2010 where notifications were not sent to these clients. What changed in E2010 SP1 RU3 is that this situation is more likely to occur because of code added to support coexistence in cross-premises environments, i.e., users within an enterprise both on-premises and in the cloud"
Unfortunately, I was on the receiving ends of both RU3 disasters, corruption on 2007 databases as well as the Outlook and BES issues with 2010 due to being in the midst of a migration. This unfortunately caused some rather visible bad impressions from the user base as well as the management team, to the point where they are utterly gunshy about future updates, so I am stuck with the existing, visibly "broken" RU3's (could not get a window to remove them) for a couple of weeks until they verify everything is as advertised with this patch and then they will schedule a window.
Thanks.