The mainstream official viewpoint is "oh, yes, definitely very rude".
I think cash is awesome, tho. You really can't buy a better gift for someone than what they would get for themselves, because they know themselves and therefore *know what they want*. I think, a lot of the time, people are more concerned with looking good, showing they made the effort, showing that they weren't "tacky" enough to give cash, than they are with genuinely doing something cool for their loved ones.
I don't really get it, but people like to be surprised and do the whole gift-giving dance and guessing game. Hell, people like to go into debt and take time off work and travel around the country/world just to bicker and fight with their families. Holidays are weird.. I'm a little disconnected from the whole Christmas thing the way we do it here in the states.
Ideally, if distilled down to the very core idea, gift-exchanging would be one of two things: A) everyone gives each other cash, but there's no point anymore. B) people truly give each other gifts that money can't buy, ie: make it yourself. This year my daughter made me some guitar picks out of cardboard and plastic bits. I know they will make absolutely terrible guitar picks, but they're still totally awesome, and I will cherish them. (Funny, kids are often better at that sort of thing than adults are.)
But yeah, I like cash.