The major tumble taken by Sirus Satellite's shares yesterday clearly shows many investors didn't learn a damn thing during the dot-com boom and bust. At a time when everyone should look to fundamentals rather than hope and hype, Sirius got slammed when two analysts, including Smith Barney's Niraj Gupta, crunched its numbers and decided the company was over-valued. There is no doubt satellite radio is red-hot and showing signs of actually become a viable business but the question facing investors is how hot will it become and the potential value of the companies involved - Sirius and XM. Sky-high valuations for high-growth technology companies are part of the investment landscape but perhaps the biggest challenge facing Sirius is the danger XM will become the eBay or Amazon of the satellite-radio market. XM has obviously jumped to a big lead with 2.5 million subscribers compared with Sirius' 700,000. You may try harder when you are number two but you're still second. The five-year, US$500-million contract given to shock-jock Howard Stern may demonstrate Sirius' desperation to get back into the race. Given how much money has spent to put satellites into orbit and now spending to attract subscribers, Sirius is a risky proposition drawing investors looking for a big score.