Google: Some investments in Google X and other technologies will pay off and Google revenue stream mix will change. Size of pay-off will offset or eclipse current ad revenues.
Amazon: Revenue growth will continue for the foreseeable future. They are still a tiny fraction of their addressable market, and have a humungous moat. Amazon will achieve profitability not by raising prices, but by squeezing suppliers (a la Walmart).
Facebook: Zuck does not think the best use of capital is reinvestment into core Facebook (see investment in WhatsApp + Oculus). That's fine, but has no track record of success with this. Oculus is very promising, but I was much more excited about it when it was a standalone company and John Carmack et al were equity compensated. The addition of Abrash is exciting though. I think this could be Facebook's Youtube if they play it right, but still not going to change Facebook's 5yr+ trajectory.
Apple: I largely agree with Fred Wilson about commodification of hardware.