My new green card (a.k.a. permanent residence card a.k.a. alien registration card a.k.a. I-551) arrived today. The conditional status has been removed and I am now a fully fledged permanent resident of the US, with all of the viral tax obligations this privilege carries.
For example, if I return to The Netherlands and do not surrender this card, I am still bound by US law to file tax returns and, if my earnings overseas are high enough, pay tax to the Internal Revenue Service, even though I would no longer be living in the US. In fact, if I keep my green card too long (8 years out of the last 15), even surrendering the thing ceases to be an option for the purposes of avoiding the tax obligation.
Anyway, since I've only held a green card for some two years now, I needn't worry about this particular problem. With the arrival of this new, unconditional card, that's me finished with American immigration bureaucracy for the time being. This card doesn't need to be renewed until 2015, by which time we'll be long gone and living in another country.