Why do people always mention this? You pay income taxes at vesting as if the entire stock was income. cap gains is only for the difference between vest price and selling if you hold it for a year.
I know of a non-zero amount of people though in the US hit by the low withholding on RSU's and then having a big tax bill, based on their value at vest before a stock drop.
Unfortunately this is usually insufficient in most companies and one will likely still owe a big chunk of change to the IRS each year as a result.
One can ask for extra withholding, but it's a bit tricky to figure out until one has worked for a given company / comp level for a given year.
F, N are cratering, Amzn is sideways, Aapl is still way up yoy (seems vulnerable this earnings season though), MSFT has been good historically but worse this year and seems vulnerable. Google has had a good run recently but is weak this year, however P/E is already in a better place than its competitors so it has room to run I'd say.
This is gonna be a wild few years ahead of us one way or another.