I have been banned from goodreads for placing a book on my "nope" shelf. No warning, no nothing. Banned.
ETA: I got an email from GR today (18th February 2015) admitting that the review they banned me for was glitched and was caused by a problem that caused my private notes to show instead of being only viewable to me.
They replied today saying... "Thank you for your reply. We have been working on issues related to the problem you reported and we will continue to look into fixing it.
However, we will not reinstate your account.
The Goodreads Team"
So even though it wasn't my fault and they are admitting it wasn't my fault, they won't undo the ban.