Actually the real investment for Microsoft wasn't the stock purchase but the commitment to keep Office on the Mac for X number of years. Without that, the Mac

Actually the real investment for Microsoft wasn't the stock purchase but the commitment to keep Office on the Mac for X number of years. Without that, the Mac probably would have tanked before the iMac ended up saving Apple. Retaining Microsoft at that time was key to retaining legitimacy. There's an awesome talk with Steve Jobs where he goes into it - it's been posted on Hacker News many times.