Paul Allen, who co-founded Microsoft with Bill Gates back in 1975, recently posted a review of Windows 8 on his blog that detailed the good, the bad and the ugly about the latest version of Microsoft’s operating system.

Windows 8 won’t go on sale until later this month, but it has already been beta tested by legions of Windows users. Allen acknowledged that “the new tablet features in Windows 8 are particularly bold and innovative” and admitted that he was impressed by “its clever integration of a bimodal interface to simultaneously support both desktop and tablet use in the same operating system.”

However, Allen added that he did “encounter some puzzling aspects of Windows 8.” He pointed out that the bimodal user experience can “introduce confusion,” particularly when two versions of the same application, such as Internet Explorer, are opened and run simultaneously. However, he added that the switching problems can be alleviated by changing file and program associations in Windows.

Allen also points out that the new tile interface in “Windows 8 style,” formerly known as Metro, may confuse some users. In addition, Microsoft has eliminated the Start menu, along with the clock, and users have to go through two steps instead of one to power down or restart their computers, or put it into sleep mode.

A new Charms bar offers access to important features such as search, share, start, devices and settings, but is not necessarily easy to find. “The availability of the Charms bar isn't obvious, as there are no visual cues as to how you display it,” Allen wrote. To invoke the Charms bar, he noted tablet users need to swipe inward from the right side of the screen. Desktop and laptop PC users will need to move their pointer to the right-hand corner—either top or bottom—until the Charms bar appears, or use a keyboard shortcut (pressing the Windows key along with the letter C) to display the Charms bar. The Charms bar doesn’t exactly sound enchanting.

Allen overall praised Windows 8, saying he is “excited about Windows 8 and am confident that existing Windows users will feel the same after they have had a chance to use it.”

Having seen Windows 8 in action recently, the new interface does look pretty spiffy. But as PC World advised, users might be better off waiting until Microsoft ships the first Service Pack before upgrading to it. SP1 is likely to fix the initial bugs in the operating system. Otherwise Windows-using accountants and accounting firms might end up dealing with the kinds of bugs that made Windows Vista such a painful experience for many of its initial users.