another possible clue is the Cracked Sapphires in his Armor, (loaned my book to a friend, so i can't quote) but notice how Saedas mentions the fact that 8 of them where Cracked? now that might just be battle damage... or he could be Tapping them, to help power his Foolish stunts (race against Daliner near start of book, he was quicker, and took that vertical leap, then lept off the tower, and survived) also, Jalena also had a cracked gem, after one of her soulcasting attempts...
oh, another thought stuck me, when Sezth was fighting Galivenr(sp?) he noticed how Quickly Gal recovered, and moved. now this is Sezth, full of Stormlight, bouncing off the walls like a rubberball, and Shard plate only enhances your strength, and endurance, not reaction time. perhaps Gal was also a near-Raident, and was taping some of his gems? (which after the fight, quite a few of them where Cracked as well)
crap... we better check on the Cousins, it sounds like that entire family was tapping gems, and doing things they shouldn't...