In a nutshell they said that it's a demo version (demoware) disguised as a learning tool. File loading/saving is limited to a special format that only PLE can read. Rendering is limited to one cpu, output is limited in size and has a giant watermark on it. This same watermark is all over the view ports too. The reviewer says that is so obtrusive that it makes modeling/working in PLE very difficult and that he got a headache after about 15 min.
Here is a screen shot.
http://redeye.free.fr/maya\_learning\_edition.jpg
There is more info and images in the article. I'd suggest that you register (it's free) and read the rest. It only takes a second.