I really like the concept of this addon, but I appear to be having some trouble with it on the 3.1 servers.
These bugs have been found by testing Prescription in a 2-man raid group. I am a druid and my friend is a mage and we were both idling in Ironforge.
1. It seems to check for all four categories even if I only tick off eg. flasks.
2. I had Prescription tell me locally who was missing buffs, but it never reported what buffs my friend was missing nor did it ever whisper him.
3. Checking only for flasks and buffing myself with Mark of the Wild would stop the feedback from appearing. The feedback is the message I receive after a check with who is missing what. It is like the buff would stop the check. Might be the same with other buffs.
Additionally, it would be really nice if I was able to disable all raid chatter from Prescription. The whisper notification should be fine for having forgetful raid members redo their buffs.