Another limit that Microsoft has in place is a hard limit on the amount of RAM you can have in a “Netbook”, or more specifically how much RAM the “netbook” edition of Windows will tolerate. In this case, it'll allow an absolute maximum of 1GB. You might think that's plenty for a “Netbook” - but we all know that the hardware demands of systems change rapidly, and when a “netbook” version of Vista is released I am sure it'll be anything but RAM-friendly.
Microsoft could change this restriction in the future, but why have it in the first place? In today's world, 1GB of RAM is really not that much. Even a desktop user with an office suite, an IM app, a few minor programs and content-laden web pages can push themselves up to the wall with a mere 1GB available.