I am moving to the Netherlands in 3 weeks and expect to be playing online from there shortly thereafter. I have done a lot of research, and actually spoken to Dutch tax consultants, and I have yet to find a definitive answer. Here is a brief timeline of major developments of Dutch online poker taxation:
1) Here is a summary regarding the recent tax scheme that was implemented by the Dutch government in 2008. It involves a flat 29% tax on net winnings on a month-to-month basis:
And here is the tax form used to report this income:
2) Here is an article from February 2012 claiming the Dutch government has forced two particular poker websites to stop serving players from the Netherlands:
3) In the end of May 2012 a Dutch court ruled that the tax scheme outlined in (1) above is in violation of the treaty of the EU.
4) Also in the end of May 2012, and seemingly in response to the ruling made in (3), the largest online poker site, PokerStars, moved all of their Dutch players from their .com site to their .eu site (with servers located within the EU) to supposedly eliminate the tax obligation for Dutch players:
I check in on a Dutch online poker forum from time to time and it appears most people are continuing to report and pay taxes monthly even given these recent developments. I really have no clue what to do once I start playing there...