I have never noticed any difference and i leave mine in a glass bowl in a drawer not sealed.
As far as the pills are concerned, i could be wrong, but its not the pseudo that goes bad but rather the additives that they put in them in order to control the rate at which the pseudo is released into the body. They have some really complex formulations using several different types of methods. This is also one of the reasons for the ever changing pill formulations. Check out this file it is quite interesting and useful.
http://www.pharmanet.com.br/pdf/drugdelivery.pdf (http://www.pharmanet.com.br/pdf/drugdelivery.pdf)
This is from the first page:
The number of products based on new drug delivery systems has significantly increased in the past few years, and this growth is expected to continue in the near future. Recent advances in the field of genomics have accelerated research of biopharmaceuticals, and today a large number of companies are busy developing protein and peptide-based drugs. These biopharmaceuticals present challenges to drug delivery scientists because of their unique nature and difficulty in delivery through conventional routes. Therefore, future research will focus on the delivery of these complex molecules through different routes, including oral, nasal, pulmonary, vaginal, rectal, etc. This review is an up-date on some of the existing drug delivery technologies for oral controlled-release, delivery of large molecules, liposomes, taste masking, fast-dispersing dosage forms, and technology for insoluble drugs. Nasal, pulmonary, vaginal, and rectal routes also are briefly reviewed.