The book "Moving Towards Stillness" mentions of a karate master whom after 7 decades of practice finally comments that he has just understood the outer forearm block. Here we are after several years, or maybe a few more than that, practice commenting as if we know shihonage as it was meant to be. No disrespect, I'm just thinking out loud here.
Anyway, I guess we should not blame the tools here if our shihonage fails. A tool is after all only as good as its handler. Thus, a good technique will fail miserably if used by an unskilled person. Of course the skill intended is subjective and does not represent a generalised mastery level of all your techniques. (you may be bad at shihonage, but you may be a master of ikkyo for example).
Peter... I agree with your comments on balance breaking (although us aikikai ppl do it a bit differently then the yoshinkan ppl, but hey if it works...). And Erik is spot on about the bad middle. I've been to iron out that wrinkle for ages now. I think I just lack basic kaiten practice. I'm top heavy and lose touch of my center everynow and then.