Coding challenges are not a waste of time when interviewing someone

It depends.
Your candidate doesn't need to know something that is a Google search away. He needs to know however to implement them, why do we do this and that and will to build his experience and focus around your methods. He doesn't need though to remember the programming language's specific library.

@lostinmyworld by challenge I meant a "take this away, build it however you like and send it to us in 3 days" style challenge.

Couldn't agree more that an interview should not be about whether or not you can remember every single line of code you've ever written

@practiseSafeHex oh ok, yes. That's a nice way to test someone. The only minus is that if he already works somewheres, he will have limited time. Nonetheless, this is a nice approach.

@lostinmyworld ah yeah I always try take that into account. Take something that should take 1 day and give 3 - 5