I view them as sort of a password to get past a gate-keeper. I tried posting job ads without puzzles in many places. I was always inundated with emails from a) recruiters b) people on unemployment who were required to apply for x number of jobs c) foreign candidates wanting visas d) others who didn't read the ad criteria.

Our last hiring round, I placed an ad on craig's list with no return email address. The only way to apply for the job was to solve a trivial programming problem. Solving the problem gave you the email address to send your portfolio to. I got no recruiter responses. I did get responses from people across the country who didn't want the job, but had fun with the puzzle. Those weren't a waste of time for me because I generally enjoy talking to fellow developers.

Puzzles may be silly. But, they can also be a lighthearted way to do a first screening of potential candidates. And, I honestly feel better about having people program something I can't use for financial gain - that way I don't feel I'm taking advantage of people that I have not yet hired or paid.