Have you seen this: www.ebay.com/gds/Fake-Nokia-N900-Now-Has-Surfaced-Updated-01-20-2010/10000000014391506/g.html? Is your N900 like the ones described?
But anyway, since you are running the Maemo5 and even installed CSSU, I think it's enough proof that it is genuine although with fake accessories.
And the N900 is designed in Finland and made in Korea, not China.
Congrats on your purchase.