ARS Technica heard the new taskbar in Windows 7 will be mandatory, just as in Office 2007, there won't be a legacy mode.
It's not a surprise that the most disruptive Windows UI change in 15 years comes under the watch of the man largely responsible for the Office ribbon. The ribbon was a jarring change for many users, yet there was no option to turn it off, which made sense to most of us here at Ars. Many people vehemently disagreed with this decision, and we expect to be hearing from them again on the new taskbar. Sinofsky told us that there will be no ability to enable the old taskbar since, in Microsoft's opinion, the new taskbar's leap in usability negates the need for a "less-able" option. While there's not quite as much ingrained taskbar knowledge as there may have been for the various Office toolbars and menus, we expect that this change will be the source of lots of contention.
The Office change seems to have given Microsoft some insight into how its customers will react to disruptive changes, and made the company a little bolder with Windows itself. Ribbon users generally took between 48 hours and 25 days to see productivity gains, and Microsoft is quick to point out how much time many Office users actually spend in front of Excel. The implication is that an aggressive taskbar change won't be quite as hard to adapt to as the Office ribbon may have been for many users.