A recent New York Times piece on the rebranding of 3M's Post-it notes has this interesting backstory:

In 1967, a 3M scientist, Spencer Silver, invented a glue with a slightly granular surface that prevented complete adhesion, but the company could not find an application for the underachieving adhesive. Then, in the early 1970s it introduced the Post-it Bulletin Board, essentially a photograph of a cork bulletin board coated with the substance and to which pieces of scrap paper could be attached.

That idea failed when people realized how much dust such a sticky bulletin board could accumulate. The article continues:

Then Art Fry, another 3M scientist, was practicing with his church choir and grew frustrated that slips of paper he used as bookmarks kept falling out of his hymnal. So, using some of Mr. Silver’s adhesive, he made sticky bookmarks, which evolved into notepaper.

The congregation, by the way, was North Church, a Presbyterian Church (USA) congregation in St. Paul, Minnesota.

Blessed be the glue that temporarily binds...