These days people trying to predict when the tech bubble will burst tend to argue it will happen when 1) tech companies run out of all the money they’ve raised or 2) the global economy worsens.
On the first, I think it is important to consider some differences from the last tech boom. By and large, today, companies raising huge amounts of money aren’t locked in wars of attrition, spending cash in ways that force down returns for everyone. They are, by my estimation, either sitting on the cash or trying to spend in fundamentally accretive ways. I think very few companies are playing the bubble 1.0 negative gross margin game which Fred Wilson recently warned about.