En el foro oficial hay 2 temas sobre los bugs que trae instalar la demo sin tomar precauciones. Yo cuando la instalé moví todas las carpetas del juego de archivos de programa y documentos del usuario
http://forum.thesims3.com/jforum/posts/list/437745.page
http://forum.thesims3.com/jforum/posts/list/437793.page
Esto es lo que ha dicho Twallan en su foro
"My mods are *NOT* compatible with the Create-A-Pet Demo, and I do not intend to do any work to make them so (I will be waiting until the full Expansion is released).
In order to get the application to work on my setup, it was necessary to rename the "The Sims 3" folder in your "My Documents" to "The Sims 3.old".
At the minimum though, you *must* rename the "Mods" folder to "Mods.old" to hide them while you are running Create-A-Pet.
Change the folder name back when you intend to play the full game.
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WARNING:
Due to issues with uninstalling the Demo product, it is advised that you back-up your content folders prior to running Create-A-Pet for the first time.
Renaming the entire "The Sims 3" My Documents folder (as mentioned above) should stop any badness from occurring.
Have Fun. "
En otras cosas, yo creo que según los datos de la demo, los caballos salvajes, venados y mapaches no aparecerán en los barrios tipo downtown, solo en los tipo base, y el embarazo de las mascotas será mas corto, de unos dos días.