I want to encourage users to register on my website, so as a registered member perk, the ads would be removed, so I was thinking of implementing AdSense in a div that slides out from the bottom of the page and has a Close button (for non-registered users). Would either of this be against Google's TOS?
I did look at the Adsense TOS, and guess what ... here's what I found in clause 5, subclause (ii)
(ii) edit, modify, filter, truncate or change the order of the information contained in any Ad, Link, Ad Unit, Search Result, or Referral Button, or remove, obscure or minimize any Ad, Link, Ad Unit, Search Result, or Referral Button in any way without authorization from Google;
Unless you can get this authorization from Google, I guess this is not possible.
I guess another method of doing what you want is to NOT generate the display of ads (instead of hiding them at the browser level) for your paying customers and display the ads for non-registered users.