I don't have a diabetic dog, but I do have a diabetic cat. So far, she's doing great with her insulin shots 2X a day. I think she's been getting them for about 4 years now. You do need to be very careful about giving the shots at the same time of day. The vet said that the "window" is about an hour early. We have accidentally forgotten to give her shot on time, so we just adjust the time of the next shot so that it's 11 or 12 hours later. You also need to make sure that your doggie eats right before having the shot to make sure that the glucose level is at its highest to prevent too low blood sugar. If you do notice that your pet is acting strangely and suspect blood sugar that's too low, you can rub a little karo on his gums.
We bought a glucose monitor (FREE from CVS with a rebate - watch for them)so that we can test her at home. It saves on vet fees when she needs a periodic check. I think it took about 6 months of ramping up her dose to find the one that worked for her. Then, we had to adjust again 6 months later when we tested and found that her blood sugar was too low. With pets, it's not an exact science. What works at one point, may not work at another point.
We haven't had any of the other issues that the other posters have spoken about. Maybe we've been lucky or those issues were more related to that pet's age than the diabetes?
I wish you the best with your doggie!