Personally I don't see the point of NOS unless you've got a seriously built motor used purely for track stuff. With that you can squirt it before the stupid-big turbo kicks in so minimising lag almost completely, so that makes sense. On a road car I see it as pointless as leaving it to squirt in one go gives you shove in a straight line (so on the motorway then) which is just daft, and having it add a bit all the time is just wasting money as you'll be refilling it all the time (depending on tank size, of course). If you want a solid 100BHP then go FI, if you want more then go FI + internals, if you want a bit more poke from a standard NA engine then get a new/piggyback ECU that'll give you what you want safer and cheaper.
All IMHO, of course.