I'll go ahead and chime in as far as ratings are concerned. :)
Under 'Rules': Content Rating of Images
* The art must fall within our ratings of G through PG-13. Artwork that is R or X-rated is not allowed.
* ArtSpots users can raise or lower the maximum rating that they want to see in the gallery. Be respectful to your fellow users and give images the appropriate rating.
o G: Contains no sexual themes, nudity, bad language, or drug use.
o PG: May contain suggestive situations implying sex or violence, mild language, drug references, use of alcohol and/or tobacco, or mild/fantasy violence.
o PG-13: May contain mild nudity (no “below the belt” frontal nudity, must be non-sexual, non-suggestive, and not the focus), stronger language, mild drug use, or mild bloody violence.
So, just to stay on the safe side, you may wish to rate http://bobbie-the-jean.deviantart.com/art/Painted-Egg-75073158 as PG-13 on AS.
http://fc37.deviantart.com/fs37/f/2008/264/3/4/344703240c245766d83ed2881b4d8498.jpg This would be PG-13. "mild nudity"
http://bobbie-the-jean.deviantart.com/art/The-Furry-Venus-75070433 (LOL, this one amuses me btw XD) is the only one that I'm not entirely sure about. Since it is a spoof of a classical piece of art that would be found at a museum, I'd go with PG. :) But if you feel like it should also be PG-13, then choose that rating if it makes you feel more comfortable.
http://bobbie-the-jean.deviantart.com/art/Inaki-Commission-75064022 This would be G.
http://bobbie-the-jean.deviantart.com/art/Low-gravity-73858418 This would be PG-13 "mild nudity"
Do keep in mind that if your (or anyone's, for that matter) descriptions contain harsh language, that would be cause for changing the rating to PG-13, even if the picture itself could be G. Just to let you know. :3
If you have any other questions about ratings, feel free to ask! ^^