I refuse to link to Ancestry which I belong to. I have never yet found a link to Ancestry,com on here that doesn't send me to an advertising screen (my membership is to ancestry.co.uk) . It is infuriating especially when it decides that I really want to go to ancestry France because I'm in France at the time.
I put the citation with as much detail as I can, including the reference number from the original repository and now also put 'viewable on ancestry.co.uk'
Re copyright, apart from Jillaines point about the terms and condition of the pay sites. This is a site that has members from outside the US and not all documents on Ancestry originate from there.
The National Archives for the UK makes clear that images from 'their' documents (which includes the census) are not to be reproduced on the internet without permission.
"You must obtain permission from the Image Library of The National Archives for the reproduction of copies of any records, whether they are protected by Crown copyright, are non-Crown copyright or are out of copyright, for publication, on the internet, for broadcasting, for exhibition or for any commercial purpose"
I recently used an online French municipal archive to find a baptismal record. The terms on that site permitted reproduction on the internet but only on payment of an annual licence fee based on the number of times the document was viewed.
It can take longer ( and in the case of wills, it can take a very long time) but transcribing the information and including that in the profile or as part of the citation allows all the information to be included without infringing copyright. (Magnus has also suggested this in his answer below)