Bubble nests: What are they?

You may have seen your betta, (if you have one), swimming in his tank with a large mass of bubbles overhead, and thought, "What in heaven's name is that gunk?" I know I did. When I first saw it, I immediately whisked away the tank and cleaned it thoroughly. Later I found out, however that these bubbles are not the product of harmful water conditions, etc., but rather the sign of a happy, healthy betta. Male bettas make these bubble nests to keep the little baby bettas in when they're fry. Males make these by breathing air in, then exhaling with saliva. Like when you make spitbubbles! Except these are more durable. I've heard that it's fine if your betta doesn't make these, but I recently read that no bubble nests may be a sign of bad water conditions. Either way, it's good if your betta makes these.
Bettas also will make these when spawning. Say, when you put a female in front of a male in his tank, but out of his reach. I have yet to see my male doing this.

P.s. My female Ollie sometimes has suspicious little bubbles lacing the surface of her tank. ???

P.p.s. Click the bubble nest photo to enlarge.