Good stuff! Had tried that, and have some suggestions:
1) The configuration is very un-intuitive - I needed to resort to reading PDF to make some sense out of what I can change there and what is the result expected.
2) Another thing (not as easy to fix) is that if you have multiple files open in VS, after the checkin VS will display the dialog that the files were changed externally (since policy changes them right before checkin). The only way to handle it I can think
of is to integrate into VS (though am not sure there is easy way to tweak the dialog off).
3) If the policy is evaluated, but check in does not happen (e.g. on clicks on policy tab in pending checkins window), keywords line will get added. Not sure how you can handle that better from the policy - that may be the limitation of the mechanism itself
Again, thanks for releasing this.