I think Oranges prices are steep - but maybe this is the way the other networks will go? At least it appears there will be room for all the netwroks to drop their prices if they want - I'm assuming they aren't tied to any kind of contract from Apple.
For me personally if Orange did unlimited for, say, £20 a month, I still wouldn't take it simply because any friends I have with an Orange IPhone have very poor 3G coverage, especially when they are at my place.
I've had an IPad in the UK since the launch, and I will definitely consider a 3G one too, but if all the plans are like this then I won't bother.
I agree with the comment about O2 (or anyone else who hasn't announced their prices yet) have an opportunity here if they have some nounce to clean up.
For example, O2 offer their own wi fi hotspots of (Cloud and BT Openworld) for IPhone customers. I think they should offer a package, say £10 a month, for free Wifi hotspot for the cloud and BT connection to the IPad, that would be enough for me.