There are reports that Google sold only 135,000 Nexus One phones in the 74 days since it started shipping. You may ask why 74 days - it's the time it took Apple to sell 1 million first generation iPhones. Motorola sold 1.05 million Droid phones in the same time frame.
They say that this is a disappointment for Google, but we have to remember that the phone is only available online and only for T-Mobile (although that is now changed). Also Google is a company that has a lot of patience and hopefully they'll continue support and development of their phones.