The clinic and GI that my daughter has is one that doesn't endorse the use of 5ASA's at all.
She used to be on the Imuran/Pentasa combination, but they insist that Pentasa in useless and stopped prescribing it to her quite some time ago.
It's interesting to me that there seems to be to different schools of thought on it's use. You'd think that there would simply be evidence of effectiveness or not.