As for 4), it looks like it was indeed very important for Facebook. Here's a quote from Steven Levy's book "Facebook": For months, the two companies had been f

As for 4), it looks like it was indeed very important for Facebook. Here's a quote from Steven Levy's book "Facebook": For months, the two companies had been feuding over the way Facebook was scraping data from Hotmail and MSN Messenger products. Facebook had its own complaint—as retaliation, Hotmail had begun labeling invitations to join Facebook as spam. According to The Facebook Effect, Moskovitz said that this caused a 70 percent drop in new users. Later on when Microsoft buys a stake in Facebook, they stop classifying the invites as spam.