The Steam Subscriber Agreement now reflects the recent legal decision in the European Union forcing Valve to offer a refund policy for Steam games. As of now, Steam users in Europe have 14 days to return games (thanks MCV). A post on Reddit does note, however, that this is a little tricky, as it sounds like part of the checkout process asks for prior consent to waive this right to finalize your purchase, so it sounds like actually playing a game ends the ability to return it. Update: According to IncGamers, this policy actually took effect last summer, and was only noticed now because of wording changes, which includes the addition of the language about waiving that 14 day period. They point to this comparison between the new EULA and the old one to illustrate the point. Here's the policy in eye-searing capital letters:

ALL CHARGES INCURRED ON STEAM, AND ALL PURCHASES MADE WITH THE STEAM WALLET, ARE PAYABLE IN ADVANCE AND ARE NOT REFUNDABLE IN WHOLE OR IN PART, REGARDLESS OF THE PAYMENT METHOD, EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT.

IF YOU ARE AN EU SUBSCRIBER, YOU HAVE THE RIGHT TO WITHDRAW FROM A PURCHASE TRANSACTION FOR DIGITAL CONTENT WITHOUT CHARGE AND WITHOUT GIVING ANY REASON FOR A DURATION OF FOURTEEN DAYS OR UNTIL VALVE’S PERFORMANCE OF ITS OBLIGATIONS HAS BEGUN WITH YOUR PRIOR EXPRESS CONSENT AND YOUR ACKNOWLEDGMENT THAT YOU THEREBY LOSE YOUR RIGHT OF WITHDRAWAL, WHICHEVER HAPPENS SOONER. THEREFORE, YOU WILL BE INFORMED DURING THE CHECKOUT PROCESS WHEN OUR PERFORMANCE STARTS AND ASKED TO PROVIDE YOUR PRIOR EXPRESS CONSENT TO THE PURCHASE BEING FINAL.

IF YOU ARE A NEW ZEALAND SUBSCRIBER, NOTWITHSTANDING ANYTHING IN THIS AGREEMENT, YOU MAY HAVE THE BENEFIT OF CERTAIN RIGHTS OR REMEDIES PURSUANT TO THE NEW ZEALAND CONSUMER GUARANTEES ACT 1993. UNDER THIS ACT ARE GUARANTEES WHICH INCLUDE THAT SOFTWARE IS OF ACCEPTABLE QUALITY. IF THIS GUARANTEE IS NOT MET THERE ARE ENTITLEMENTS TO HAVE THE SOFTWARE REMEDIED (WHICH MAY INCLUDE REPAIR, REPLACEMENT OR REFUND). IF A REMEDY CANNOT BE PROVIDED OR THE FAILURE IS OF A SUBSTANTIAL CHARACTER THE ACT PROVIDES FOR A REFUND.