I used to run an abandonware game site when I was in high school during the first dot com bubble, and we would get paid $100-300 per month from advertisements on the site, which paid for us to run it.

After the dot com bubble crashed, we were getting paid $20-30 for the same ads and more traffic. It forced us to take the site down, as we didn't have enough revenue to fund it anymore (we kept the ring up though, it's still in operation today, probably with some of my code still under it's hood: http://abandonwarering.com).

Here's my question: Let's assume this is a second bubble for the sake of my question. After that bubble crashes, if advertising revenue tanks with it, how much does that tear into the profitability of these companies that depend exclusively on advertising?

I'm not a gold bug, but I remain highly concerned about the heavy burn rates and artificially high private valuations in the industry right now. Something I've learned from experience is that if it feels too excessive, it usually is.