How effective are directed attacks?

I've read a lot of discussions about how there are regular attacks by various foreign governments, most typically attributed to the Chinese or North Koreans. At the ACSAC conference last month, Ron Ritchey from Booz Allen gave a fascinating talk about how they tracked down a series of targeted intrusions into major US defense contractors. I'm pretty surprised how much detail he was willing/able to give, especially since this was an unclassified setting. I'm even more surprised that he was able to share his slides, which are well worth reading.

Is this paranoia, or are these attacks for real?