Let me dig it up, but IIRC there was a divine power gish wizard that abused this, and made it virtually impossible to fail at anything, and the enemies virtually impossible to succeed.
EDIT :
[spoiler]The Fortune-Teller -- He Tells Fortune What To Do
Cleric (Luck and War) 1 / Wizard 4 / Runesmith 5 / Divine Oracle 2 / Fatespinner 4 / Fortune's Fool 4
I've played a build similar to this, and it's actually rather amusing to play. Very amusing. The sheer amount of rerolls you get can be pretty insane, and when the DM smirks as his power-attacking-for-full red wyrm rolls a natural 20 and is about to x3 crit you... you just nicely ask him to reroll the die. Or when you roll a natural 1 on a save-or-die, and you realize you have five different ways of getting out of it (Luck Domain, Luck Feat, Luck Feat that turns 1s into 20s, Fortune's Friend, Not This Time (Living Greyhawk only))... you just have to smile.
When you can control randomness to that extent, it's actually a very powerful mechanic. In higher level play, if you can average out all the dice rolls, it takes almost all the risk out of the game -- people don't die from 8s and 12s; they die from the 1s and 20s. With no 1s and 20s, the party cleric can estimate pretty accurately how much health everyone is going to take each round ("ok that dragon does 80 a round...") and compensate for it. But when you get crit, and that 70 point bite turns into a 210 point bite... that's when the tank dies, and the whole thing goes straight into the pot. Controlling randomness is incredibly powerful.
Additionally, Fortune's Fools can take an extra swift action a round (as long as it's a luck maneuver), which is key for gishes who should be casting quickened spells every round. And if they want to go nova for a round, Fatespinners can boost the DC of a wail of the banshee by 4, and then force a reroll on a survivor. Or he can just spend his spin on attack roll bonuses or saves.[/spoiler]