no, i wouldnt ski at all.  your spleen is enlarged when you have mono.  Your spleen filters toxins out of your blood.  You can live without a spleen, but your body wont recycle the iron in your body nor filter your blood.  I went to high school, with a two girls who lost their sister when she went waterskiing with mono.  Is your life really worth not missing a couple of months of skiing?  Take it from a guy who has had mono 3 times.  I got a pretty good understanding on this topic.