Yes. I started when everyone on my team was doing it at one of our practice races. The stuff most folks use is 3M "77". It not only eliminates flapping numbers, it also makes it one heck of a lot easier to pin the number. Without glue, you are trying to get it so it is pulled reasonably flat, which involves some amount of guesswork. With glue, you choose the right position with your jersey spread out on the car seat, spray the number, stick it on, and put the pins in as a backup, and because most organizers insist they be used. Be sure to pin it so the head of the safety pin is into the wind, and not cupping air!I wanted to ask you - do you use spray on contact cement to adhere your number to your jersey?
As far as positions go, you see all sorts of things. If you position high, you can feel it under your arm, at least until it softens up. Pin it low, and you can't access your pocket. Towards the middle is more aero than the side, but that only matters if you aren't glued. And most importantly, you don't want to cover any team or sponsor names! I've evolved towards low and to the side, unless I need the pockets, in which case I move it up a bit. The glue is great. The numbers come off easily, and don't seem to leave residue when the jersey is washed. And, as I learned from Hermes (who no doubt positions his pins in the aero position), you pin through the number itself, not through the punched holes! Of course the absolute best way would be to have the pins inside the jersey.
When there is a bike number required, that is usually heavy paper/cardboard that folds so there is a number on each side. I glue the sides together, making it nice and stiff, then attach it to my saddle/post. With my current saddle position not leaving any rails behind the saddle, last event I glued the cardboard around the seat post, then used the twist ties for safety. It was actually pretty aero that way, since it formed a foil shape. Some people use tape around the seatpost, and some have permanent solutions, like plastic that attaches to the bike, with the numbers glued to that.
I'm providing detail, because this is the kind of stuff that can be a big distraction, and thus a stress factor, until you've done it a bunch. Having to handle the numbers is one reason early packet pickup is nice: one less thing to worry about pre-race!