@ Navigation: Particularly important for groups such as the FARC, which operates in the jungle and mountains regions of Colombia and Venezuela, or for groups (such as Hamas), which have been known to conduct waterborne raids.
@ Detonators: Some GPS systems will allow you to input the location you want to reach, and then tell you when you get there, which could easily be adapted to interact with a simple detonator, setting off an IED. This would make it easier to deliver vehicle borne IED attacks, since you wouldn't have to recruit a suicide driver; you could just ask someone to run your vehicle somewhere (some such attacks by involuntary suicide bombers are known to have taken place, but the detonation has been by remote control, which is subject to interference).
@ Attack Coordination: Equipping terrorist bands with GPS systems would make conducting complex attacks by several different forces easier. The use of GPS by terrorists to facilitate navigation has been reported in the open press. There have been no press reports of other uses.
@ Cruise Missile. GPS, in the hands of someone with a degree in electrical engineering, enables you to turn small aircraft in cruise missiles. This, however, takes more effort than most terrorist groups have shown any appetite for. But the potential is there.
Terrorists have long used commercial technology. But it's interesting to note that Islamic terrorists, despite years of dire predictions, have not been able to get the most out of the commercial technology available to them. Criminal gangs and non-Islamic terrorists are another matter. Radical Buddhist terrorists in Japan have used commercial technology to manufacture nerve gas in the 1990s, and drug gangs often create very sophisticated communications and transportation systems in support of their manufacturing and smuggling operations.
Terrorists have been adopting GPS technology more aggressively of late. In recent months, troops and paramilitary forces fighting terrorist in several widely separated theaters (e.g., Iraq, Colombia, and so forth), have been capturing more GPS devices. That should not be surprising, as GPS locators are now widely available and cheap ($40 at Radio Shack), they are very easy to use. The value of GPS to terrorists includes,