nijuu: I always thought if a game was regionally restricted for anything on Steam for your region you simply werent able to purchase the sucker at all ie it will show as not available in your region etc?
There are, last I recall, 4 types of regional restriction on Steam now.
1 - Point of purchase. Most common form. You simply cannot buy it in your region (should be playable in most cases).
2 - At first time activation. Mostly affects retail keys, but can affect Steam gifted/traded copies from certain regions (namely some RU versions). Game cannot be added to an account or undergo first time installation. Can be bypassed with a VPN and won't cause problems during subsequent launches.
3 - At launch. Whenever you go to play the game, your region is checked and if the check fails, you can't launch the game. A VPN is needed every time you want to play the game. Can sometimes by bypassed with the Steam Appid text file trick in conjunction with launching from the exe directly (but must be run once via Steam first - same applies when a patch is released). This mainly affects specific regional retail activated copies.
4 - Full on IP Block. The game is placed in a permanent "pre-load" status without access to pre-load files. Even if you install the game from a valid region, it will not show up in your Steam client as installed when in an affected region. This is the type of block that usually gets applied to Japan (examples: FEAR 3, Kingdoms of Amalur, Mafia 2, etc.) for several months at a time and affects all copies of a game, regardless of where it was purchased. Like No. 3, can be bypassed with a combination of VPN, Appid text file/offline mode.
Also note that, if a game has a staggered regional release, you cannot play the game until the release in your region. So if the game releases in the US first and releases in the UK last, and you get a US copy gifted to you in the UK, you still need to wait for the UK release. Further, if that game isn't being released in your region at all and you get a US copy, you still need to wait until after the UK release before it becomes playable.
Now, it gets even more annoying when Valve only applies one of those blocks and not related blocks. Again taking FEAR 3 as an example; it only had the last block applied to it. That meant you could buy it from a third party site that was selling it in Japan and activate it on Steam without error while connected to Steam with a Japanese IP address. Only then would you find it couldn't be interacted with. Of course, as it activated on Steam without issue, third party sellers couldn't refund it. Valve claimed the keys were for the US only and not for use in Japan. They had no answer as to why they allowed such keys to be activated by Japanese IP addresses, nor could they provide a legitimate reason as to why they felt they were allowed to deny access to a game being sold by third party sites with the permission of the publisher.
So yeah, regional restrictions on Steam are now far more confusing than they used to be. If you trade games via Steam, this is something you should be aware of as Valve will not refund/remove region locked copies of games even when traded to a region it cannot be used in. Further, they don't tend to differentiate the region locked copies from other ones via the trade window.