I've got an Innotek 300 that I use on Tipper, my half Weimeraner, half Husky. It has been invaluable to me, although I only use it in very limited circumstances.
From what I can tell, the only thing she inherited from her mother was a pretty good tolerance for cold weather. Otherwise she looks like Weimeraner with too much brown and some white patches. And the hyperactive nature as well.
The only time I use it is when she (A) doesn't come when called (which usually means she's racing after something's scent), or (B) she's playing too rough with my other dog - a 15+ year old Collie mix who adopted me after somebody dumped her on my road.
Now this model Innotek has 7 shock levels, plus a tone. It also has two different probes, the only difference being the length to compensate for our friends with longer fur. With the collar on, all I have to do is hit the tone and she immediately stops and comes running. I'm currently working to transfer that behaviour to a dog whistle with a fair amount of success. On the other hand, she must be almost immune to pain. I've found that I have to start at a level 5 pulse just to get her attention. This model does both the quick pulse and a continuous shock. The continous shock self-limits to 10 seconds, and then can't be used for 10 seconds afterwards. Most of the time the pulse is enough to do the job. For cases where additional reinforcement is necessary (such as chasing after visitor's cars when they leave) I've found it necessary to hit level 7 on continuous for a second or two. This enough to make her yelp and then run straight to "daddy" for forgiveness. I also have to make adjustments for water. She loves my creek, but once she's been playing in it, I've found that a level 4 pulse has the same effect of level 7 for a second (gee, whodathunk wet skin would be more sensitive /forums/images/graemlins/blush.gif), so I have to make certain that I adjust the level accordingly.
I think the key to one of these is to not overuse it, but at the same time use it consistently. Just like djradz's dog, Tipper actually looks forward to me bringing it out of my pocket, for it usually means she gets to spend the better part of the day outdoors (with decreasing supervision, and she's only 5-1/2 months old!). I may go an entire weekend and only "zap" her two times. She's quite intelligent, and a fast learner.
But I will be so glad when she outgrows the puppy stage (which I hear for Weimies, is somewhere around a day or two before they die /forums/images/graemlins/grin.gif). Just this past Tuesday, I thought I was going to have to seek out an opthalmologist. When I went out to her pen to give her her morning rub down before going to work, she jumped up once and caught me by surprise, raking her left paw down my face, ripping off my glasses, and scoring my right eye with a claw. For the first hour, I feared she had at least scratched my cornea, it hurt so much. Fortunately that turned out not to be the case. And I don't fault her at all - there's not a mean bone in her body, she was just so happy and bouncy to see me.
Jerry