The mobile chip *should* be unlocked, its not guaranteed, but it should be, even if its not, you can always pop/cut L6s, and then set a different max multiplier.
The NB mod/BIOS upgrade will be needed for nForce2 owners, while the VIA and SiS chipsets seem to change the multies just fine on the fly from within windows
Mobile cpus also run at a lower voltage so it runs cooler than the desktop cpus. I guess it saves on electricity too. I notice that the XP2500+ mobile default fsb is 266MHz.. The desktop 2500+ default fsb is 333MHz.