I'll second these responses in that my magnificently fluffy 2CE also magnificently kicks my ass as 20mg and others' asses at less than this amount. A friend of mine found around 7mg of this stuff to be too much.
I had a lot of fun with this stuff when it arrived. After measuring its mass and placing it into the jar that I intended to use for storage in solution, I played with it for a while. I used a spoon to condense it all into a relatively dense white-powder. Then, I jiggled the jar and watched it fluff back to its original form.
I don't doubt the possibility of unusually weak batches, but I think it's just as like that these reports are due to individual variation, tolerance, poor measuring techniques, and other factors.
As an example, an acquaintance of mine obtained a separate batch of 2C-E. 13mg of said batch provided him with a strong experience. 15mg of this batch was among his most intense psychedelic experiences. At the same time, 30mg of this batch when given to his girl-friend produced "a mild trip". This same girl-friend of his reported a "stomach-ache" with no significant psychoactive effects from 50mg of another drug 2C-I. That 2C-I was from my own supply which worked just fine in the 15-20mg range for the rest of us. His girl-friend is either a hard-head, or has a serious psychological block.
Okay, point to be taken is that there most certainly is dramatic variation from person to person. I'm beginning to witness this with pretty much all psychedelics, though, phenethylamines are more notorious for it.