Windows celebrated two birthdays this week. Windows XP was a decade old on October 25, and Windows 7 marked its second birthday on October 22.

Both operating systems have been insanely popular. In computing terms, XP is downright ancient, and yet it still accounts for roughly half the installed base of Windows users worldwide.

Meanwhile, Windows 7 is selling briskly. It’s earned overwhelmingly positive reviews, and the massive Windows user base is slowly but surely embracing it and moving inexorably away from XP.

Those two products represent high points for the Windows family, but there were plenty of low points in between. In fact, an unvarnished history of Windows over the last decade turns up its fair share of failures and big mistakes.

As a longtime Microsoft-watcher, I’m as fascinated by the company’s missteps as I am by its successes. Anyone who worked at Microsoft in the first decade of the 21st Century knows the impact that those wrong turns had on the company and its culture. How the company responded to those mistakes had an indelible impact on products that are on the market today and those that are planned for the future.

For this list, I deliberately ignored everything that happened before the public launch of Windows XP. That means, thankfully, we don’t have to rehash Microsoft Bob or Windows Me, nor do we have to go through the long and painful antitrust trial that ended earlier in 2001.

But that still leaves plenty of history. The ten case studies I've gathered here represent a mix of security gaffes, bad business decisions, and user experience failures.

They say every mistake is a teachable moment. So what has Microsoft learned from its miscues over the past decade?