My post is long-winded, sorry.
This is a good discussion. It's nice to see the board utilitzed for something other that bellyaching, and RJ pilot v. Mainline Pilot flame wars.
When I was instructing, I always noticed how the slip seemed to be a "lost art" in flying light aircraft. You'd get someone for a flight review and ask them to demonstrate it, and you'd get the 1,000 NM stare.

Followed by a resounding, "Huh?"
For those currently instructing in Cessna singles, here's a little exercise that will surely become an eye-opener: When the student is on the downwind leg of a suitable runway, tell them they have an engine fire and the flaps have become inoperative because the fire has burned through the wiring at the battery and/or the CB popped and cannot be reset. Ask them to follow the engine fire procedure to a forced landing without the use of flaps. Unless they are familiar and comfortable with the forward slip, they will likely end up too high, too fast, and in an overshoot situation. The sight picture is WAAAAYYY different without flaps! And pilots will invariably end up pointing the nose down while slipping... hence the extra speed. I've seen guys come out the no flap-forward slip at over 100 knots, and they have no Earthly way of making a safe landing on a 5,000 ft. runway. After a few practice runs, they get the hang of the sight picture and they become somewhat proficient at putting the airplane down safely in the first 1/3 of the selected field.
Now you might say, "Yeah smart alek, but the Cessna engine fire checklist calls for a dive in excess of 100 knots! Of course the student is going to go too fast!!" Well, you'd be absolutely right on that point. But that is why this is such a great exercise. It not only teaches airmanship skills, it helps develop good judgement. Seriously, are you going to follow the check list and fly the airplane at 120 knots into the ground because you want to put the fire out? Of course not. (How many times have you CFIs given a student an engine failure at altitude and watched the following scenario transpire: The student selects a landing area, the student gets buried in the emergency checklist, the student finally completes the emergency and forced landing checklists and has no idea where the selected landing area is, the student finally identifies the selected landing area and realizes he/she cannot make it there because we are now too low to glide to it. Good thing the student flew the checklist!

) There comes a time when you have to decide when to accept the fire, have a safe landing, get out, and leave the machine for the insurance company to deal with. Also, when you cut the fuel and mixture, you're pretty much going to cut the fire. Remember the fire triangle from grade school? No fuel, no fire. Besides, that's why Cessna built a firewall. So again, this becomes a great exercise in developing airmanship skills and judgement.
BTW, do not brief the student before hand. Instead, use this exercise to demonstrate how one can really get themselves in a pickle without regular recurrent training, familiarity with equipment, and solid basic airmanship skills. Most students (and especially pilots who are in for their annual or biennial flight review) will appreciate learning additional skills like this. I have often had flight review folks decide to come back for some additional training in other "scenario" type of training exercises... something that was non-existent back when I was learning to fly (e.g. I simply learned power off stalls and that's it, but when I started teaching others, I taught traffic pattern procedures at altitude, leading to a power off stall with a designated "hard deck.") Anyway, this type of training usually led to a discussion of the "FAA Wings" program, and I often had the same students return for the 3rd hour in the program. Do they still do the "Wings" program?
Forward slips were an integral part of learning to fly gliders. My glider students would get pretty good at the "jammed spoiler" landings and could easily put most powered aircraft pilots to shame!
Another neat trick for intructors involved the collusion of ATC and the words, "Go around." But I don't want to let the cat out of the bag on that one. CFIs feel free to send a PM, and I'll spill the beans.
Thanks for reading.
Respectfully,
RightBettor, CFII-ME-G, Gold Seal (still got it too!)