The bundling that got them convicted of monopoly abuse - including Windows Media Player with windows, so that they could sell a video streaming server for which the client program and browser plugin were already installed (where competitors like real and quicktime had to offer a separate download). Similar story with IE (netscape's server product was actually amazing for the time, with ideas that were only beginning to be adopted ten years later).
Selling IBM an OS that they hadn't actually written yet - you could argue no harm no foul, but MS's actions meant IBM was taking on much more risk in that contract than they realized.
They also had an infamous habit of announcing vapourware alternatives to competing products, knowing that many potential customers would hold off buying if they thought a Microsoft-developed alternative was in the works (e.g. PenPoint OS vs Microsoft's Windows for Pen Computing - the latter of which had very minimal functionality when it finally came out).
I never understood the crying over that. If you have a good product available right now, and you can't sell against a vaporware product that may or may not be available for year(s) in the future, you're simply not good at sales, or your product isn't good.
At Zortech, we found selling against vaporware to be easy sales.
