I completely know how you feel. Still, I tend to err on the side of latitude, and remembering that kids did not ask for their lives and time to be so divided.
For example, I hate portable video-game machines. I feel like kids (OK, our kids) spend more than enough time on the Wii and computers at home and should not be watching TV or playing video games while they're driving in the car, or walking next to you in a store, etc. I do not want them to lose the art of just TALKing and BEing with other people!
So I was annoyed when DSS's Mom sent his PSP, to use at our house. But weighing my preferences and instincts about parenting against his perceived right to use and enjoy what his Mom bought him, the latter seemed to carry more weight. It doesn't always. When he was teetering between sometimes doing well in school and other times being a slacker and she bought him an I Hate School T-shirt, I felt that my parenting instincts carried more weight than her desire to be the "cool" parent and his BFF. But as far as the PSP...if we let him do SOME video-game type things anyway, we don't have to have complete control over it. He can play them on his PSP sometimes, if that's what he worked out with his Mom.
But our basic house rules still apply: He can't play games we don't allow (M games, or any where you're beating women or hunting down cops...hopefully those are all M!); and he can't be on it all the time! We don't have to be totalitarian and say he can't ever use it, because we don't like it. But he is still not allowed to replace interactions with family and friends, and playing outside, with some electronic device stuck in front of his face. (So I think he finds it more gratifying, to have the PSP at his Mom's...)
Perhaps you could let your SD bring the item to your house, if she wants, but still have sensible rules about where/how she's allowed to use it, so it doesn't get broken or completely trample your way of life.
If it's more a matter of teaching financial priorities and you don't like the message it sends, for kids to own one of these, I DO think it's possible to discuss different values without denigrating the other parent. I do it all the time, since we are very middle-class and my ex (my teenage sons' Dad) is very wealthy. I don't want my sons - as they make their way in the world and decide for themselves what their views and priorities are - to think we live the way we do only because we can't afford to live like their Dad does. I mean, certainly SOME of how we live is because we can't afford better, but I want them to understand that even if we could, DH and I would not buy new cars, or vehicles that cost as much as some families' houses; and that the reason they don't each have a giant, flat-screen TV on their bedroom wall is NOT JUST because we can't afford it! I preface discussions with a reminder that I like their Dad & Step-Mom very much and think they're good parents; and that there's more than one valid way to look at the world. I want the boys to understand mine, but that doesn't mean their Dad is BAD, if he sees things differently from me.