Microsoft’s Windows Vista lost market share last month for the first time in almost two years, a sign that users are already abandoning the oft-ridiculed operating system in favor of the new Windows 7.

According to Web metrics firm Net Applications, Vista dropped 0.2 percentage points during September to end the month at an 18.6% slice of the operating system pie. It was the first decline for Vista since a 0.3 percentage-point slip in January 2008.

Windows 7, meanwhile, gained 0.3 percentage points, its biggest one-month gain since Microsoft began handing out the new OS to the public in January 2009. Windows 7 powered an estimated 1.5% of all computers that connected to the Internet last month, also a record. Its share means that about one in every 67 personal computers is already running Microsoft’s new operating system.