I am currently working full time (40 hrs ) under CPT (spring 2008), clearly written in I20. In addition, there are many of my friends working 40 hrs this semester under CPT. There is one of my friend who did full time CPT for two consecutive sem (2007 fall and 2008 spring). However, my college doesn;t allow students to participate for full time CPT for 2 consecutive semester.

Finally, if you take full time CPT during a semester, you neednot take any course for that semester. It counts as a full time student.

So, I think the whole matter depends on the college  and your degree too.