8. Death By A Thousand Versions Of The Same Product. How many versions of Vista are there again? Okay, if you say so. We only need 3 versions of Windows 7: a home version, a business version, and a mobile version. Three products, and three SKUs. That's it. Give us any more and we'll send you back into timeout, Microsoft.
10. Annoying The User. UAC was the direct approach. Ask the end user at every turn possible a question they don't care about, don't know the answer to, for something they are going to do any way. Or there's the indirect approach, the sum of a lot annoying little problems: slower file copy, a slower computer using experience, a lack of drivers, stability issues, confusing product editions, etc. Either approach works great at annoying the end user. Doing both guarantees it will happen.