When I saw my first PC with an alternate, quick-boot Linux operating system (DeviceVM), I was impressed. But I no longer think this is a viable market. I do not believe consumers want to run two operating systems on their computers--one fast to boot but limited, and one slow but capable. They want what they know, and for most of them, that means Windows. That's why Windows XP has become the popular operating system for low-spec Netbooks. And with computers on the whole getting more powerful, and Windows 7 getting such great reviews even on midrange PCs now (which will be low-end in months), I just don't see much of a market for two-OS computers.
Xandros does claim some unique points for Presto. It has full access to files stored in the Windows partitions, full access to networking hardware, and there's an app store for programs that run in the platform. Also, unlike other quick-boot products, Xandros claims Presto doesn't require any hardware integration work.
It's probably a fine operating system by itself. For it and other Linux distros, there are popular browsing and communication apps available, as well as decent (and free) productivity suites. The Xandros OS makes more sense as a competitor to Windows, not an adjunct to it. That's a niche market, as everyone knows, but it probably has more of a a future than the market for pre-Windows operating systems.
If you want to try Presto, it will be only $19.95 when it ships in April. The beta is free until then.