We have some much troubles about that in France (school, work and ... message boards) and a lot agree on the fact that it's because of the use to write short messages on mobile phone. SMS langague.

I remember a student of my husband a few years ago who wrote on his copy something like 2morrow ..... my husband was really angry ! and when he asked him to explain how you can do sometihng like that at 21 years old he said he didn't even notice it and does that all the time .... :s