The Swedish Tax Agency wants every Swedish gamer that earns money from online-gaming to pay tax for the money earned. There are a few games where you can earn money in-game for example Second Life and Diablo 3. The gamer needs to register all earned money from gaming to the tax agency; but this isn't that easy since the gamer needs to know who the buyer is.
The criteria for the tax is that the seller is from Sweden and that he is a person that can pay taxes. This means that if the gamer is selling items on an online auction house, or something similar; he/she needs to find out who the seller is, and if the seller can pay tax, then report this.
There won't be that many sellers reporting this income to The Swedish Tax Agency. This law seems pointless to me, would be nice to see a follow up on this from the tax office next year to see if there was actually anyone paying taxes for their earnings.
Source: Read the full standpoint in this matter. (Article in Swedish, use google translate to read it)