Not sure I'd do that on any stock...you need your savings in case something bad happens (and things always happen in life, right?). I wouldn't invest any money I couldn't afford to completely lose...I believe SIRI will do well and grow, but it's not my savings or official retirement fund.
Of course, if it grows into a multinational media satellite company with a billion subscribers across the globe and a stock price of $650 per share, I would definitely cash that in and retire...lol