On the upside, product placement can provide support for good, but ratings-deprived series.
The Office is a prime example--I'm convinced NBC sticks by it not because of critical acclaim, but because of the way it awesomely does product placement in huge, obvious ways.
There have been two complete episodes invaded by Chili's, including a hysterical sendup of a Chili's manager ("We do not tolerate excessive drinking. That patron is no longer welcome.")
The iPod placement was more goofy, but definitely fit the storyline (Secret Santa with inappropriate gifts).
I've also recognized Sun Chips as an important plot point ;)