Depends on whether or not Linux can get its act together within the next few years. Distros today are light-years ahead of their predecessors.
With Microsoft fumbling Vista, and with things like viruses and spyware (both unsolicited and Microsoft’s WGA crap) I can both Linux making inroads in the business world at least (Macs will do better with consumers).
If someone could get a push for Ubuntu running machines in schools in place of overpriced macs or just unreliable xp boxes that would expose people at a younger age and get more kids interested in open source.