I haven't experienced issues with the app emailing my contact list, so I'm not able to comment on that. I have had the problem of the app crashing every now and again, but it doesn't bother me to much.
This app does a lot of things right: it provides free, nice quality images for use on an iPad screen. The images are updated practically every day; after I went through the several hundred images the first day I downloaded it, I only have to look through the first three or so pages to make sure I didn't miss any! As for content, this app really runs the gamut of themes, from cute animals and cartoons to nature images and abstract art.
What I would like to see is maybe an option to filter images based on some kind of tagging system, such as "nature" or "cars."
A tip for current users: make an event (if you use iPhoto) with all of your backgrounds and sync it to your iPad. That way, you can have all the ones you like with you for when you want to change your background!