I was a longtime user of TypeIt4Me, the first Mac app that did this sort of thing. TypeIt4Me is really the granddaddy of these sorts of apps, but unfortunately, like a grandaddy it has sort of gotten a little slow and outdated. I switched to TextExpander because of expansion issues with TypeIt4Me, issues that I brought to the developers attention and he could not fix. Basically it couldn't keep up with me when I was typing fast and would expand words in the wrong place. I have only used TextExpander for a week, but I have not once had the same issue. Also, I have found the user interface more intuitive. TypeIt4Me is still a great product, so it is worth checking out if you are in the market for this kind of utility, but for now I have happily made the switch and would recommend TextExpander.