When the client and the server machine have different communication protocol lists you can experience serious delays when the client tries to instantiate an object on the server, and you can even get an error if the two protocol lists don't have any protocol in common.
For best response times, use DCOMCNFG.EXE on both machines to ensure that both lists include the same protocols and that they appear in the same order. If possible, ensure that TCP/IP is the first protocol on both the protocol list on the client and the protocol list on the server. Remember that you need to reboot the machine before your changes become effective.
Another easy and effective tip for optimizing DCOM operation: delete all the protocols that you don't really need.