Tech Stock Diagnostics
Bill Burnham has a Top 10 list of signs that a software company is in trouble. Most of them involve analyzing the company financials (high DSO, declining deferred revenues, etc) although I've found this one is usually pretty close to the truth:
The head of sales and marketing leaves.
If the company fires the head of sales and marketing it generally means that he is going to or has been missing his numbers. If the sales and marketing head resigns on their own, it generally means that they think they are going to miss their numbers or can make more money working somewhere else. Either way, it’s usually bad news for the company over the next couple quarters.