We have seen manufacturers using desktop Pentium 4 as a mobile CPU to lower cost but it is more interesting to use a mobile Pentium 4 as a desktop CPU.

Vr-zone.com has an article up on how to run a mobile Pentium 4 on a normal desktop board and increase the FSB above 200Mhz on air cooled to achieve 100% overclocked. Other interesting findings on how Speed Step Technology and multipliers are being implemented can be found here