A memory leak has been found in Microsoft Exchange Server 2010 SP1 which effects the Microsoft Exchange RPC Client Access service.
Below is an extract from the TechNet article…
A memory leak occurs in the Microsoft Exchange RPC Client Access service on Microsoft Exchange Server 2010 servers. When the memory leak occurs, the “Process(Microsoft.Exchange.RpcClientAccess.Service)Private Bytes” performance counter keeps increasing. In this situation, the memory leak causes memory pressure on all the servers. For example, the RPC Client Access service on the Mailbox server causes memory pressure on the Microsoft Exchange Information Store service. This memory pressure reduces the effectiveness of the Information Store caching. Therefore, the performance of the Mailbox server decreases.
Note: This memory leak is more rapid when an Exchange Server 2010 server is used with BlackBerry Enterprise Server (BES).
To fix this issue, you will need to apply Update Rollup 3 for Exchange Server 2010 Service Pack 1.
Update 1: It would seem that you will need to apply the update via http://update.microsoft.com as the download link is not working at the time of writing.
Update 2: It would appear that the download link on this is dead for a reason. Anyone with RIM Blackberry devices should be cautious and contact Microsoft if they are having the issue in this blog post. http://blogs.technet.com/b/exchange/archive/2011/03/14/exchange-2010-sp1-rollup-3-and-blackberrys-sending-duplicate-messages.aspx
Update 3: Microsoft have released an updated patch to fix both the memory leak and the issue with BES. Full article can be found here.