Google is making excessive use of their GeoIP database these days to test new features in a limited area of their choice. Now they decided to only let users from the US use the street view option in Google Maps. If you live in another country, you'd actually have to wait until Google releases the feature worldwide or use a proxy from inside the states.
There's another way to avoid Google's IP filter though:
Add &gl=us at the end of the URL !
And for all you non-believers, here's a screenshot of me walking around in New York City while I am actually sitting in Germany writing this post: