> Do today's VCs take technical due diligence seriously? If not, why not?

Because they're worried they'll miss the boat. Maybe less true in these not-quite-so-booming economic times but not so long ago VCs were literally competing to get in on rounds of funding for hyped up startups. The fact that the hype often never amounted to anything didn't seem to matter, if so-and-so was investing then you wanted to be in on that too or you'll look bad.