Seed collection: How the pros do it

I found a thread where a respected seed collector talks about about collecting, cleaning, testing, and storing seeds at the Scottish Rock Garden Society Web site. Fascinating stuff.

In most cases, she does say that seeds are to be "dry stored in a cool, dry place ... Shelf life can vary from a few months to some years, with the average being 1-2 years. All seed that tolerates dry storage is an ideal candidate for storage in the freezer, both short and long term. Seed must be completely dry, ideally packed in paper and placed in freezer containers with tight-fitting lids" (PDF).

So while it doesn't address the whole paper vs. plastic thing directly, it does provide some insight into what critical factors for seed storage success.