We're a YC-12, VC-backed company. We were profitable within a year of the seed round. We still have the bulk of our Series A in the bank but went ahead and raised a $40 million Series B because terms were extremely good (low dilution plus we can ride out any downturn). I suspect some of these high valuations are simply investors paying a premium to buy in, not an expectation that the company is or isn't worth that much.
When I walk around SF with my PlanGrid shirt on it isn't other people in tech that say hello or know who I am... it's the guys working at construction sites. People in hard-hats and boots who tell us our software has changed their lives.
The tech press and insular SV community obsesses about the ultra-unicorns. Some of us are just busy quietly solving people's needs (usually in industries that have been long-ignored by SV/tech) and we're doing quite well for it.
There may be a bubble but if you build something that provides real, immediate value to customers then the rest of it is just noise.