MrsCB - yes he did, in the context of children using it, I believe. The timing could have been better, obviously, given the record breaking launch of the Instagram - and it probably would have been a good idea for someone to have got in touch with the previous holder of that username prior to the launch! The whole launch is rather one of those things which should have been positive all round but it doesn't look as if anyone had really paid attention to the very small details, which are always the ones which end up causing an issue.
Security costs would likely change very little if we were to be come a republic. Presidents are hardly cheap!