Cat's tail language

I have been told and have even read that when a cat holds her tail in  a vertical position and the end of the tail vibrates it means that the cat  is very happy. This has intrigued  me because in the 5 years my Cucumella has lived with me she has never done this and yet I have the impression that she is very contented and happy. I have never known her to have any aggressive gesture towards anybody, she is very sociable even with visitors she has never seen before.  She walks around almost permanently with her tail right up with end of it curling towards her back but there is no vibration at all.Could this be a wrong interpretation?  

My kitten's tail flies straight up like a broomstick when she sees food (which is when she's happiest ). The other one's tail goes straight up and curls at the tip when she's happy and interested, neither of their tail have ever vibrated. I think they are just mellower or lazier or, I think those sorts of guides are general guides and you just have to get to know your own cat's tells.

One thing that makes me smile so often is the way my kitty struts around with her bushy tail sticking straight up.  

Noodles does the "happy tail" thing; but I don't think I've ever seen Mooch do it.  And I can't really recall my other cats doing it either. I think its just one of those personality things.