I saw this thread a few days ago and now seeing that it has developed into a longer discussion I thought I would chime in.
I see that the OP has made a decision and I think that if it suits her family that is great.
However, she
did phrase the question to gather opinions.
I do feel that it is unforgivably tacky to let a pre-teen use an electronic device at the dinner table.
A PP stated that lots of adults, couples, children etc use electronic devices at tables in restaurants, so therefore it is a common practice but not necessarily a proper practice.
Oh god now I'm going to feel old....when I was a child (honestly it wasn't that long ago LOL, I'm 24)...it was not accepted to play with GameBoys during dinner.
Sure, I was allowed to colour with crayons...until I was 5. From then on my parents taught me about carrying on a proper conversation, enjoying the experience of dining, taking in my surroundings etc.
CG isn't exactly a boring place. You could request seats at the sushi bar and watch Yoshie work her magic, you could request a table near the open kitchen and see the flames rise and the chefs in action. You can request a table near the window and see the sunset, the electrical water pagent, wishes, the castle changing colours, the astro orbiter spin, the boats on Seven Seas Lagoon. There is plenty going on to stimulate when conversation has been exhausted.
I am an iPhone addict. I LOVE it and use it constantly. I take pictures in the parks and post them live to my blog etc. But at dinner, it sits in my purse because it is rude to use it at the table.
The only electronic device I have at my dinner table is my camera. I write dining reviews, so throughout the evening I take pictures of the food. This actually *creates* conversation as I ask those I am dining with what they think of their meal. However, I never use a flash as it could distrupt patrons at the next table.
At Victoria & Albert's all cell phones are banned. You are not allowed to have them on the table because it can be disruptive and could ruin another diner's evening.
When the OP first posed the question it brought to mind an episode of Two and a Half Men. Jake has a DS like device with him throughout an entire episode, he even brings it to a funeral, and it ends up in the casket

to me this was a commentary on how the use of electronic devices is getting to be too accepted - and that is coming from someone who grew up in the tech era where new gadgets were (and still are) an obsession.
OP, I am glad you made a decision that you feel is best, but as you phrased your question in such a way as to gather opinions, I will say that I would not do it myself and that I do feel it is tacky.