From the "you learn something new every day" category:
Ok, I have to admit I did not know the correct phrase for this is "on tenterhooks." I thought it was tether hooks or something like that. Don't ask me what a tether hook is or why I thought that. I just did. Apparently the commonly misused phrase is on tender hooks. But that too is wrong, wrong, wrong.
You can find more words that are commonly "confused, abused and misued" in this article from Ragan's Grapevine: Tips & Tactics From the World of Employee Communications.