I think the coffee that comes out of single-serving coffee pod machines is not very good. But, putting that aside, it can be obscenely expensive, as Oliver Strand points out in the NYT:
For example, the Nespresso Arpeggio costs $5.70 for 10 espresso capsules, while the Folgers Black Silk blend for a K-Cup brewed-coffee machine is $10.69 for 12 pods. But that Nespresso capsule contains 5 grams of coffee, so it costs about $51 a pound. And the Folgers, with 8 grams per capsule, works out to more than $50 a pound.
Your average bag of "expensive" artsy coffee runs around $20 a pound. Not to mention the environmental costs that come along with chucking hundreds of millions of plastic capsules into the garbage.
There is a much better way to use a Keurig, though—the reuseable My K-Cup lets you brew your own coffee in Keurig machines, so at the very least you have fresher coffee that's cheaper, and there's nothing to throw away after every cup. (Here's some non-Keurig alternatives too, if you're interested.) [NYT]