In the past, a clustered MSMQ service could only listen on one IP address. This was because MSMQ depended on the network name which in turn could only depend on a single address.
In Windows 2008 the address dependency has been changed and now you can have multiple IP addresses:
"One of the new features that Windows Server 2008 failover clusters introduce is the ability to locate cluster nodes on different, routed subnets. Therefore, Client Access Point (CAP) configurations have cluster network name resources that depend on multiple IP address resources."
This will allow you to use one clustered MSMQ service to handle messages from different subnets where in the past you may have had to use multiple services in different resource groups, one per subnet.