I used personalized touring plans for every day of my last trip. In general, I found it to be helpful to get a broad idea of just how much you will be able to do during a day or a half-day in the park (and it forces you to make decisions about what you will forego). Going in, I knew that I wouldn't stick to it minute-by-minute, but I planned on using it is a guide, which is approximately how it ended up working.
As PPs mentioned, the biggest flaw with the personalized plans is that they don't have good estimates of wait times for M&Gs (with a few exceptions like Mickey and Princesses, and Tinkerbell). As a result, if you want to do lots of M&Gs, it's probably not a good tool to use (unless you do as PP suggested and schedule in breaks for the M&Gs). A related note is that is seems to always list the wait for the Little Mermaid show in DHS as 7 minutes. When we were there we had to wait about 45 minutes for this (not because of a long line, but because we had to wait until the next show started).