Bad question unless you ascertain the candidate knows enough about Adwords to give a good answer. (Whether a candidate should know enough about your core products is another question...)

What would you say during an AdWords or AdSense product seminar?

Bad question, again requires product knowledge a candidate may not have.

Who are Google's competitors, and how does Google compete with them?

A little broad but could be made into a good question.

Why do you want to join Google?

Waffle question that should be used as filler.

What do you know about Google's product and technology? Have you ever used Google's products? Gmail?

If answer == no/nothing, kick candidate out of room.

What is the most efficient way to sort a million integers?

Poor question but asking general "how would you approach problem X" questions isn't too bad, at Google product managers need to be pretty technical.

How many golf balls can fit in a school bus?

Poor question but estimating similar product-related issues is good and they essentially break down into the same types of answer as golf balls, gas stations in the USA, etc.

How many times a day does a clock’s hands overlap?

Terrible, should never ask something the candidate may have already worked out in the past and which does not require much thought to answer.