[MaryFromMichigan]

...average amount of time spent at the screen per session, ranging from 1 hour to more than 8 hours at a time.

Guess freepers have one more thing to worry about.

[Wooly]

I tend to agree with this study as a very heavy user.
I also have noticed another thing that happens to heavy computer users that almost mimics dyslexia in as much as when typing you will start to change the order of letters in a word without noticing it. Example The will be typed as Teh but the user will not notice it.