ETTR makea sense mostly at ISO 100. With Canon however, it makes sense at ISO 200-800 as well. The idea is to let as much light possible but still keeping the highlights you want to keep. This is not easy since the histogram may show clipping but the RAW may not be clipped. Also, with certain colors like red, that color channel may be clipped even if the histogram looks OK.
I keep my 5D2 at EV=+1/3. This is a lazy way to expose a bit to the right, and to compensate for the conservative metering of my camera. When the SS is not a problem, I would overexpose a bit further until I see a brighter shot on the back screen - how bright - it is based on experience, not on the histogram really. This is very important (to me, anyway) for shots with a high DR or for ones which I expect to pp heavily. Sometimes I blow the highlights, unfortunately. My most viewed shot on Flickr has severely blown highlights.
The benefits of ETTR is not only lower shadow noise but lower shot noise. With strong pp, WB tweaks, vignetting corrections, etc., that noise may become visible even at ISO 100. With crop cameras, it takes very little to reveal it.
At higher but moderate ISO, it is better, for example, to shoot at ISO 800 to the right, if you can keep the highlights, than at ISO 400. The reason for it is - well, it is a Canon sensor. The read noise at ISO 800 is roughly speaking 1/2 of that at ISO 400 but you get no benefits form lower shot noise, of course (same exposure). This is counter-intuitive since you would expect that you should stick to the lower ISO if you can. You take more risk, as well, since metering in low light may not be so accurate, DR might be higher, and you can easily blow the highlights.