I bought my Nexus One outright for $529 plus tax, and pay T-Mobile $60/month (plus $4 tax) for unlimited data, unlimited texts, unlimited night and weekend talk, and 500 prime time talk minutes/month. If I'd taken the subsidy and bought the phone for $179, then I'd have to pay $80/month for the same deal. Similar plans are at least $100/month on Verizon or ATT, and $80 on Sprint.
By foregoing the subsidy, I paid an extra $350 for the phone. But over 24 months, I save $20/month or $480, so (at 0% interest) I come out ahead by $130. Also, the phone is unlocked so I can pop in an ATT or European or Asian SIM card, and talk economically on the phone anywhere. And if I was unhappy, I could sell it on eBay.
But I'm not unhappy - it's a terrific phone at a great price.