I disagree 100%. If you watch Ellen Page in interviews, you can tell that she fir perfectly into that role, and it was a very natural character for her to play.
To me, I think Juno would compare to a Napoleon Dynamite, even though I havent seen it. People either loved or hated it, and people are very passionate about the opinion they have. Its a type of humor that I call smart comedy, and some people, especially the people who are into slapstick comedy or sex and poop jokes just dont get it.