If a blocking spell can be used as a response to an attack, it also makes sense to me that it can be used as a "free action" (a response to "no attack"), outside my own turn. Using RAW rules, it is possible to perform an action (eg perform an attack) and then, as a response to an enemy's attack, use Blink and move 3 yards. The same can be performed with reversed order (Blink, as defense, then perform action). However, if no one is attacking me, it could also be beneficial to blink (for instance, to move faster) before or after my turn's action. Is this allowed in RAW? If not, it would mean that getting attacked would sometimes be beneficial, giving me "free benefits" (in this case, cover ground more quickly).
Ps: Can Blink Other be cast at a foe, for instance, to make him fail an attack and force him make a body sense roll?
Pps: Could I cast a Command or annother blocking spell to make an enemy fail it's active defense (from an attack made by a friend)?
Ppps: Gurps is great! The only thing that I don't like very much is how it handles time to performs actions (eg: attacking with a knife is as fast as attacking with a claymore). I have made some house rules to address timing issues for attacks:
http://forums.sjgames.com/showthread.php?t=139641
Similar approach could include other actions such as casting regular and blocking spells.