The biggest social networking community site in the Netherlands is Hyves (http://www.hyves.nl) (and perhaps used in Belgium as well). It's comparable to sites like Facebook.

For the Dutch hyvers: there is a Gipf project hyve. May be interesting. Not much happening yet. But it might change with you guys on board. Have a look at: http://gipf.hyves.nl/

Not all Hyvers are active or see the use of joining a hyve (like me in most cases), but if you dig this stuff, you know where to be :-)