<rant>
I won't turn mine on... don't want to and as Zeewolf pointed out above, if you are following behind someone with a decent connection, attempting to ninja their nodes will likely reduce your nodes per hour count if you're on the same route. If they land before you -even slightly- and have a decent connection, they will start and therefore finish mining/herbing before you and will get the ore/herb. If you attempt to ninja it, your toon will go through the motion and will fail as soon as the other toon succeeds. At which point, both of you mount and fly off in the same direction. All things being equal, you and him will get to the next node at very close to the same time... and try to out ninja each other for each and every node. Of course, if you have it set to off, as soon as your toon realizes that there is someone near that node, you will 'wave off' and move onto the next one, easily beating the other toon to it. Of course, if the two of you are literally on the same pattern, the two of you (and any others) will simply leapfrog over each other and get every other one available...
If you're not on the same pattern then this whole discussion is moot. I've seen others pop in and out of my route, generally only staying with me at most 2 nodes cause I'm using custom routes. (I'm going to publish some of them once they are well tested). If someone attempts to ninja one of mine, they generally fail cause my toon reacts pretty quickly... but even if they do, I may message them just to let them know there is someone watching (and see if they are... I had one message back saying 'whoops, sorry - was about to hearth back anyway'... and then he was gone... lol)
If it was up to me, the option would be removed from HB - we don't need to lower ourselves to the standards of others, especially when all it does is make us MUCH more likely to be reported and therefore banned.
</rant>