I know a number of pre-IPO Googlers, as well as a couple folks who have struck it rich with startups. For the most part, they own their own (pretty nice) home, and have little interest in owning other homes. A couple owned double homes, a big suburban one in the South Bay and either a condo in SF or a beach home in Santa Cruz that they could stay at for weekend getaways. One guy owned homes near every Google office that he would regularly travel to, but since they're in different cities, they don't do much for Bay Area real estate prices.

For the most part, people who got rich in tech tended to invest fairly conservatively in conventional index funds etc, and do a bit of dabbling in angel investing on the side. (Another unfortunate unintended consequence of the huge Silicon Valley wage increases is the near-collapse of the individual angel funding market; it used to be someone could write a check for $100K and sustain a founding team for a year or more, but that's increasingly difficult with Bay Area housing prices.) That makes perfect sense: another cardinal rule of investing is to stick to what you know. People who go into real estate because they've heard real estate is a good investment tend to get slaughtered; like any capital market, there's a lot of subtlety to knowing where, when, how much, and how to buy. If your passion in life is software, these details are going to be terribly boring, and you probably won't be much good at them.

I also know a number of landlords. Interestingly, this group is largely disjoint from the people who struck it rich with tech startup options. They are largely ordinary high-paid professionals who are comfortable with leverage. They might use their salaries (and perhaps a little inheritance) to buy a duplex, pay that down a bit, then use the rental income to justify another loan on a small apartment block, fund the mortgage with cash flow from that, pay down principal, etc. The entry into becoming a landlord is made significantly easier if you're making $300-400K/year than if you're making $100-125K.

(Interestingly, duplexes seem underpriced in Mountain View right now - you can sometimes buy an old 3/2 duplex for less than a ritzy 3BR condo. That indicates to me that a number of home buyers today have no interest in becoming landlords.)

I've spent plenty of years renting apartments from investment properties owned by rich people as well, but every single one of them has been a rich person (or corporation) who borrowed money from a bank to buy a multi-family property, not someone who cashed out a startup and invested the proceeds in real estate.