I agree it should be covered early.
Since jumps are typically initiated between two arrows pointing out, if you followed the line and arrows that are permanent, someone else's jump should not be a problem. If someone puts arrows on their jump line, I guess they could screw up other divers, especially one with little experience. Hopefully no one is that dumb.
On a jump placed where there are no double arrows, that shouldn't be a problem as the person placing the jump needs to mark the line as well. Once again, I guess a dumb diver could improper mark their jump. This one seems more likely to be a problem then the first example since someone could do it virtually anywhere after the reel is tied into the mainline. The person making the jump could also forget to place a marker on the exit. Any suggestions on how to handle this type of problem? It's something I haven't really given enough thought to.
A T is a totally difference situation from my limited experiences with them. I have only seen the T used once IIRC. That was in Hole in the Wall at the mill pond. I haven't been back to Peacock 1 since the T was placed. Everything else for me has been the standard jump.
btw, when I mention complex navigation, it was explained to me that any time you make a directional decision, that qualified as complex navigation. That meant jumps and Tees were out. Gaps were ok (GUE cave 1 taining) since no direction decision is required. It is effectively one line. Jumps didn't cause a problem at the time as we always saw double arrows. Then again, we always had a large thick yellow line as the mainline.
edit: gaps only at sinks where you could exit.
OneBrightGator:
What if an Intro diver comes upon someone else's jump, or finds one on his exit? How to deal with T's in the line needs to be covered in Intro because if they do any amount of diving after the class they will run into them in one form or another.