Steve Ballmer said in an interview that Longhorn will be Microsoft's biggest release since Windows 95:
I think Longhorn is going to be the biggest release we have done since Windows 95. It's going to be a big thing, but I don't think we should have expectations that we will have people lined up at midnight to buy a copy, necessarily, despite the fact that Longhorn is a huge deal. I think it's bigger than anything else we've ever done--except Win95. In a sense, technically, it's much bigger than Windows 95.