Looks like there is at least one more update before Exchange 2010 SP1 is released.  RU4 for Exchange 2010 was published today.

You can download it immediately here: http://www.microsoft.com/downloads/details.aspx?FamilyID=09B4973E-3A80-4FB9-9F60-5C6E2B7A2727&displaylang=en

Or first read below for a list of issues that the update rollup fixes:

Update Rollup 4 for Exchange Server 2010 RTM fixes the issues that are described in the following Microsoft Knowledge Base articles:

979342 (http://support.microsoft.com/kb/979342/ ) An attachment is not visible when an Exchange Server 2010 user opens a signed mail message by using Outlook 2003

979517 (http://support.microsoft.com/kb/979517/ ) You cannot send a message to a Dynamic Distribution Group in a mixed Exchange Server 2007 and Exchange Server 2010 environment

979790 (http://support.microsoft.com/kb/979790/ ) An IMAP4 client crashes when accessing an Exchange Server 2010 mailbox

979801 (http://support.microsoft.com/kb/979801/ ) An error message is generated in Exchange Server 2010 when you use Exchange Troubleshooting Assistant

979810 (http://support.microsoft.com/kb/979810/ ) You cannot connect an Exchange Server 2010 mailbox by using a MAPI client

979848 (http://support.microsoft.com/kb/979848/ ) Event ID 1066 is logged and you cannot move a mailbox from an Exchange Server 2003 server to an Exchange Server 2010 server

979862 (http://support.microsoft.com/kb/979862/ ) Event ID 4999 and Event ID 7031 are logged when you move a mailbox to an Exchange Server 2010 server

979921 (http://support.microsoft.com/kb/979921/ ) You cannot replicate a public folder from one Microsoft Exchange Server 2010 server to another, and Event ID 3079 is logged on the target server

980149 (http://support.microsoft.com/kb/980149/ ) The Add-MailboxDatabaseCopy command fails when it is used to add a database copy to a Database Availability Group in an Exchange Server 2010 environment

980353 (http://support.microsoft.com/kb/980353/ ) A MAPI application that is used to access Exchange Server 2010 mailboxes crashes when the application accesses an address book

980354 (http://support.microsoft.com/kb/980354/ ) “MAPI_E_INVALID_PARAMETER” error message when you copy email messages from an Exchange Server 2010 mailbox

980364 (http://support.microsoft.com/kb/980364/ ) Microsoft Exchange Transport service on an Exchange Server 2010 server crashes when a certain message is processed

980701 (http://support.microsoft.com/kb/980701/ ) An Exchange Server 2010 mailbox user receives a NDR error message when the user sends an email message to multiple internal users

980852 (http://support.microsoft.com/kb/980852/ ) The RpcClientAccess process on an Exchange Server 2010 server crashes when you access a mailbox by using a MAPI application

981033 (http://support.microsoft.com/kb/981033/ ) Error message when you expand the Microsoft Exchange On-Premises node in the EMC of Exchange Server 2010

981961 (http://support.microsoft.com/kb/981961/ ) Event ID 4033 is logged and the Free/Busy replication from an Exchange Server 2003 server to an Exchange Server 2010 server fails

982209 (http://support.microsoft.com/kb/982209/ ) Some embedded messages are corrupted when they are contained in a message that is sent from an Exchange Server 2010 mailbox address

982378 (http://support.microsoft.com/kb/982378/ ) A delegate receives only one meeting request when someone sends a meeting request to several principals in an Exchange Server 2010 RU1 or later environment

982944 (http://support.microsoft.com/kb/982944/ ) The msExchVersion attribute value of a user is stamped incorrectly after you run the Enable-MailUser cmdlet to mail-enable the user

983200 (http://support.microsoft.com/kb/983200/ ) The .xls file as an attachment is empty when you access an Exchange Server 2010 mailbox by using OWA

983631 (http://support.microsoft.com/kb/983631/ ) “redirect it to people or distribution list” rule does not work on an Exchange Server 2010 mailbox address

2084061 (http://support.microsoft.com/kb/2084061/ ) A user intermittently fails to access an Exchange Server 2010 mailbox after the mailbox is moved