All what you describe has got nothing todo with Messenger Plus! though.
Messenger Plus! is an addon for MSN Messenger which adds some extra features; you still use and chat with MSN Messenger itself. Messenger Plus! does not replace MSN Messenger.
The delays you experience are normal (well, that is if they aren't that long). Messenger never has signed in immediatly, it always take a few seconds. And depending on various things this can take up to 30second or so. For Windows Live Messenger this is 'normal'.
The same with loading your contact list. This is actually a new feature in Messenger. It loads the contact list from the cache (because that's quicker) and after that it requests and loads the contactlist from the servers if it can. Because of this you quickly see the contactlist appearing but it wont be filled in yet and/or you can't do anything yet. So it seems that there is a lag of some sort, but actually its just the contactlist (the window) appearing quicker as otherwise.
All this said, because you installed Messenger Plus!, it can take a tad longer longer to load all this as Plus! needs to load too of course. And depending mostly on how many scripts you have, this can take a second or two. But it shouldn't interfear that much with the overall load time at all.
Now, all this is speaking in a matter of seconds, no longer than 20-30 seconds at the upper most. If it takes longer there sure is something fishy (no offense CB
) about it and the first indicates of this is:
The main window remaining when you switch to another messenger (so you use polygamy?) isn't normal. But again it is very very doubtfull that this has todo with Messenger Plus!.
If it happens with all versions of Messenger it surely indicates that there is more going on and that it certainly doesn't have todo with Messenger Plus!.
Check if you're not running some "internet security" tools or other tools which run in the background and may interfear with programs.
/ 
