I'm of a similar mindset to shiv - we have never used the iPhones or the iPads particularly regularly, but we have let them play on them from time to time on the understanding that they get put away when we say it is time.
We gave them an iPad to share for Christmas and we have been very clear on the rules - ie not before school, educational apps only during the week, any arguments and it goes away immediately etc - and we enforce them so that they know what's what. If at any point (now or when they were younger) I didn't want them to play on it I would tell them so and that was what they had to live with, rather than pretending it was broken or out of battery. I do think that these technologies are addictive, but I believe that showing them how to use them responsibly (and implementing exactly the same rules for me and dh) helps them to understand where technology sits in our lives. I have also found that mine are falling behind their peers somewhat it terms of use of ict as I would always rather they were doing something else, so having some time to practice the things that they are going to need in the future seems to make sense.