First, this series of articles is good and I won't take anything away from the author on it. Well done.

But, I agree with many of the others when it comes to bit masking. I compare it to all the problems associated with storing CSV information in a column. It's generally a violation of good database practices to store more than one piece of information in a given column and will lead to performance problems not unlike those associated with storing CSV data in a table.

Take the humble "test" problem where you want to store answers given by the person taking the test. First, the test is likely a multiple choice test and that renders bit mapped answers virtually useless because bit mapping can only have two states... not the 4 or 5 that may appear on an MC test. If you store only the fact that a question was answered correctly or not, then you've lost a lot of data. It's usually important to store the actual answer choice to try and determine why the people may have gotten a question incorrect. Of course, on a survey, it would also be important to capture the actual answer.

In cases such as tests, surveys, and maybe even control settings (which radio buttons or check boxes are selected), I'd recommend a long skinney table known as a Name/Value Pair which can be indexed for tremendous speeds and also allows for greatly simplified analysis methods using GROUP BY and other tools.