So what's the deal with GTD and Tinderbox?

Of late I've been hearing more and more about “Getting Things Done” (aka GTD) and programs like Tinderbox? Seems that there's some new management trend starting to spread. Anyone actually use these systems? Are they useful for long-term productivity improvement? Before I go and investigate this too much further, I'm interested in hearing if it's just another management/productivity fad, or if there's something real behind all this. Both the book and the software seem to be getting a lot of conversation spreading about them.