Agree with @rrhoover, if this works then it would be huge. Would be interested to know how proactive you have to be -- as in, do I just say "Monitor the Basecamp website." or do I have to set up very specific campaigns.
I've used a company here in NYC called Perpetually (now called Smarsh) who did exactly this and loved it. See: http://www.perpetually.com/
A similar tool to help you look at competitive display intelligence is Moat (think of it as "ad unit search"): http://www.moat.com/
Growth Everywhere - Mamoon Hamid of VC Firm Social Capital Shares the Secret to Why Sh*t Gets Funded
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