The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.By David Sterman NEW YORK ( StreetAuthority) -- It appears as if we've finally shaken the ghost of the dot-com bubble. The Nasdaq has been moving up sharply during the past few years and now trades at levels seen back in 2000, and a few recent dot-com IPOs are now valued in the billions of dollars. Yet as I noted in this article, investors may be setting themselves up to repeat history, assigning market values to companies that still have a lot to prove. Simply put, any company that is worth $8 billion, $9 billion or even $10 billion needs to be treated as a hot young growth stock for years to come if investors are to see any further upside. That's why I reflexively gravitate to stocks that appear to embed a much lower level of expectation. I also like to see these stocks move out of favor, at least temporarily, when a real sense of value can emerge. That's why I recently put Zipcar ( ZIP) in my $100,000 Real-Money Portfolio. It's also why I tend to hold off pursuing a recent gainer like real estate data service firm Zillow.com ( Z). Zillow's shares have risen roughly 40% in the past three months, and I'd rather check it out on a pullback. Follow TheStreet on Twitter and become a fan on Facebook. But a pair of other dot-coms is squarely in the doghouse, and their current valuations seem to sharply discount potential strong growth to come.