I'm pretty sure this isn't normal behavior. I've been running Messenger with Plus for some time now, and it's always been hanging for a few seconds between everything.
I'm running an almost pristine Windows 7 setup, after reinstalling it about two weeks ago. When I try to open the main window, there's noticeable lag. When somebody messages me or I try to initiate a chat with somebody, lag happens too. And typing in the chat window will cause random hanging as well. It's almost impossible to have a proper chat with anybody nowadays, due to the lag.
I'm only using the event logging and chat logging functions of Plus.
Well, you know how it is: if that happens without Plus!, it means the problem is somewhere else, maybe in Messenger itself. I would sugest trying to disable your anti-virus/anti-whatever software completely, reboot and see if it solves anything.