Just a quick note, I have tracked down the memory usage issue. I dont even know how this is possible, but since ive done it my memory usage has been at 20MB for MSN with a contact window open.
I used
NoRooms ListCleaner and removed all of the contacts that had deleted me from their list (there were about 80), all of the people I was allowing to see my status even though they werent on my list and I wasnt on theirs (omg, there was a lot, at least 160), and all the people im blocking that deleted me and I deleted them (about 60)....I then deleted all the Address Book Entries corresponding to these contacts...and Wallah, My Messenger Memory Usage is now down to 20MB with 1 chat window open...thats 60MB less than before I cleaned it. Even if it is a matter of simply cleaning it, they obviously need to improve upon their skills, cause a lot of people with older accounts (like mine, from all the way back before I even started coming to this community) will have a ton of these dead entries and such.
Source: eXoenDo