Yeah, Tyranny has been on insulin for at least five years now. She gets two shots a day right between her shoulders. Very quick and she doesn't even flinch and then gets lots of attention. Just pull the skin in a tent and put the shot where the bottom of the door would be, push plunger and done!
She's done very well, and I also put her (and the other cat - since they free feed) on weight management cat food (even though she's also thin). I think it's lower sugar and you can sometimes get to where you can wean them off insulin (not all diabetic cats, but some). I've not weaned her - but I think that the food helps!