Like others have said use it as a tool, i dont have mine on all the time just when i need it. I have to disagree about not having it tho, F2.8 isnt remarkably fast there are many times where i have faced situations where im shooting at 3200 ISO and still only getting like 1/10th second at F2.8 and this is where it can come in handy, anything below 1/100th of a second the slightest movement can cause blur.
But get to know what it actually does. IS only combats shake not subject movement, actual movement of the camera. So say you are shooting a still life the subject will be still and the IS will correct any movement you produce like the mirror, or slight hand movement. But if your shooting a bird in its nest at 400mm IS comes in handy without a tripod, holding a 400mm lens fully extended without a tripod for any length of time will produce some movement so it will help correct that, but if the bird is say building a nest moving its head up and down, its getting darker and your only getting say 1/60th of a second it may appear sharp, zoom to 100% and there will be some slight blur which is annoying. Same with any grinding animals, sheep/cow/cammel/giraffe while its chewing may appear still, shoot at 1/100th the body will most probably be sharp IS will have helped because it is not moving, but the head wont. The grinding causes the head to vibrate and they do this quickly so a speed of 1/500 or over is best to get a sharp pic (trick to shoot any grinding animal).
It helps to know your subject what its characteristics are. There are also things you can do, breathing techniques, similar to a sniper, holding the camera close to your body to create a tripod effect etc.
The thing i love about IS is that it is there, when it is a bit darker when you half press the shutter button and everything just stops is such a great feeling to know that it is helping. I would rather have it than be without it just because a situation will come and you wont have a tripod and the shot wont be there, or it will be heavily degraded because of a high ISO.
It is a tool, like a camera, alot of people are almost scared not to have IS now which is crazy, Photography is over a hundred years old and people have been perfectly fine. Alot of people just dont understand and have to have the best and think it will make them better photographers but in most cases that is false, having an understanding of your subject, its behaviour, how to combat a situation is key, thinking fast in situations. IS is not a miracle technology, it will not make an f5.6 lens turn into a F1.8 it will just alow you to shoot at slower speeds at smaller apertures, but your subject must be still or it still wont make any difference.
But as a tool is useful and is definitely worth considering. I always thought the same as you when it came to the 17-55mm but finally took the plunge from a 17-85mm IS and its probably the best decision i have made. The quality difference between the 17-85mm and the 17-55mm is ridiculous, its amazing how much faster and shaper it is, F4 in my opinion is too slow for a standard lens so is 5.6. I dont like variable aperture lenses for that reason SLOW!!! But the 17-55 compared to the 17-85mm is off the scale, SHARP this thing is really sharp, barely any chromatic aberration and a very small amount of vignetting at the extremes.
Your not just paying for the IS or F2.8, this lens is basically an L lens without the weather sealing. It has phenomenal quality, there isnt another zoom lens that will better suit a crop body. All the L series standard zoom start at 24mm (unless you get a wider full frame version) so you will be at 38mm with the 1.6 crop and thats the widest. Yes you can buy third party lenses but unless they are digital versions you will be in the same place with the 1.6 crop. Ive heard good things about some other lenses but at the end of the day i dont think any other standard lens can compete with the 17-55mm. I got mine a 2 month old second hand item for £550 thats £350 off RRP so look around, there are alot of people recently that go crop then decide its not for them so trade in there gear for full frame leaving some good savings for us. Alot of 24-70mm L owners are envious there is not a full frame equivalent to the 17-55mm and on a crop body the 17-55mm will outperform the 24-70mm.
Tom Scott
