I have never been on Pentasa alone, but I was on a combination of Pentasa and purinethol for a little over 6 years. The real drag was taking so many pills a day & I would frequently forget or just not be home to take all the doses I needed to take. I'd also have period of just not taking them because I felt fine, and there was starting to be evidence that maybe Pentasa didn't do anything for people.
However, on multiple occasions, I would feel bad after a while of skipping Pentasa, and go back to the full dosage. This would make me feel better again and back to good health. It became more than a coincidence during this period (at least 3-5 times), and I am convinced that I did have positive response to Pentasa.