Sharia law in the Netherlands may not be practised in an actual 'sharia court', but that makes little difference. The point is that Islamic rules about marriage, divorce, custody, parental authority, alimony and inheritance are being implemented according to the sharia, and that these contradict Dutch law.
The clearest example of this is polygamy. Marriages are made and dissolved in mosques in the Netherlands, including polygamous marriages. On September 19, 2008, newspaper De Telegraaf reported that 173 men in Amsterdam are registered as having two legal wives, two men even have three wives. A spokesperson for the city of Rotterdam admitted in NRC Handelsblad last year that polygamous marriages are being registered in that city on an almost weekly basis.
It's a pity that the national statistics bureau automatically rejects these marriages because it thinks they're mistakes. Because of this there are no national data about polygamy in the Netherlands. (Non-registered polygamy is probably even much wider-spread.)