Sometimes I type too fast for my own good. When I was in high school, they offered typing classes. I took 2 semesters of it, and although it was tedious (we actually typed on typewriters believe it or not) it has been a fantastic skill to have. I've timed myself on programs that measure that type of thing and can get between 80 and 100 words per minute.
However, sometimes my typing speed is to my detriment. I have noticed that I tend to use the same phrases quite often when I write, as I'm sure most people do. A phrase I use a lot is "about it". An example is, "I would like to hear about it." In and of itself, this is a perfectly normal, mundane phrase. However, when I get into speed typing mode, at least half the time my thumb decides to hit the space bar at the wrong time with those two words. So instead of "about it", I end up typing "abou tit". A simple mistake, but resulting in a somewhat embarrasing situation (especially when IMing to a woman, and you can't hit the backspace to correc tit before she see sit). :)