Some time ago Rob Walling, on Startups for the Rest of Us, mentioned that Datanyze is closer to real time than BuiltWith. So real time, in fact, that you can get a list of sites that have just (yesterday?) started a trial of your competitor's product, and approach them during the buying cycle.
I have a question, if you dont mind. I'm someone, who's been trying to build out simple SAAS business myself and wanted to understand the impact of using price arbitrage as a sales strategy. (which in Castor's case is dramatically underpriced compared to geckoboard and others.)
Just my experience with SaaS, usually they start with ridiculously low price to capture the market. After you have established yourself, you can increase your price and grandfather early customers. You can even force your free users to upgrade to a paid plan by stating that ("upgrade now to lock old price! limited time only!").