Ever since the late 1990s, I've been casually watching the ads on websites... importantly it's watching the same websites over time. I haven't been dilligent about it, so it's just an observation of big overall trends. Mainly I keep a rough mental tab of the types of companies placing ads. At first it was other Internet companies, then there was the .com crash and by 2002, it was mostly junk companies selling wireless webcams and other obscure junk. Then around 2004, maybe 2005, major companies started advertising on the Internet. But around 2008 or 2009, they disappeared, and it seemed like a lot of mid-range ads dominated the pages. Now, I'm starting to see major companies return in a big way. Lexus, Jeep, Motorola, Toyota, etc.
Just an observation.