Have you ever read up on that list of predefined goods? It is pretty interesting to see how regularly the list is changed and how many different factors they add in to adjust prices.

Someone did a study looking at magazine prices for example. They picked magazines because they almost always had prices printed on the cover and cover images are cataloged. I don't remember the exact numbers, but they found that the actual prices went up by a much higher rate than how the CPI calculated it because they were discounting price increase with a claim that quality got better. Meaning you may have seen the price double over time but the CPI only said it went up by 30% because you got more value from the newer issues.