Following are the two separate "best practice" recommendations from MS regarding a MSDTC configuration for Exchange cluster:
According to Exchange 2003 Deployment Guide on page number 128
Note In Windows Server 2003, it is a best practice to create a separate cluster group containing the Physical Disk, Network Name, and IP Address resources (for example, MSDTC Group), and then add the MSDTC resource to that cluster group. Creating the MSDTC resource in its own cluster group helps ensure that a failure to the MSDTC resource does not affect the overall availability of your entire cluster or Exchange resources.
Note It is not recommended that you create the MSDTC resource in the default Cluster Group or the group containing Exchange resources.
According to KB Article # 301600 (http://support.microsoft.com/default.aspx/kb/301600)
Note We recommend that you create the MSDTC resource in its own resource group, such as you would for Microsoft SQL Server, where you can do so. To do this, follow step 2 to create this new group. If you cannot do this, or if you have a light-use DTC scenario such as a cluster dedicated to Exchange Server, proceed and use the Cluster group. On dedicated Exchange Server clusters, the MSDTC resource should be placed in the default cluster group.
I believe it is very confusing. As per KB article # 301600 for Exchange the MSDTC "should" be placed in the default group. As per Exchange 2003 Deployment Guide "It is not recommended that you create the MSDTC resource in the default Cluster Group or the group containing Exchange resources." I can understand the light use of MSDTC for Exchange servers but I never came across a "shared" cluster for Exchange server. I believe it is another best practice recommendation (or industry recommendation) to use a "dedicated" cluster for Exchange. Anyone have any comments or thoughts on this?