That's a great use of Luck. Advice to that effect should be in the Judge's section. But at what point do Luck checks encroach on Saving Throws?
By the way, I forgot to mention, I'd use Luck Checks also to determine things that maybe the player forgot to specify.
DM:Suddenly, the wall crumbles and you risk getting caught under the rocks.
John: Wait, I didn't say which wall I was searching first! I'd say.. the other one!
DM: Hmm, I'd say...
... Roll LUCK.
John: <roll... 4>
I don't know if that's good or bad. I haven't formed an opinion on it. If it works for you, that's cool. But a good Luck score could make saves obsolete. At which point I'd question why we have saving throws.
I don't think that Luck makes Saves redundant. For example, back to "meeting Medusa", I'd also use Luck and Saves to avoid her gaze as it has been explained. What I think you missed, and I think Meinvt assumed, is that if you fail the Luck check to "happen to be looking the other way", you don't get your save. You're done, stone-boy.
It's like : 1st chance: LUCK, following chances SAVES.
This way even a rubbish PC whose only double digit ability is Luck has a way of surviving out of sheer luck. Sooner or later thogh, it will all come down to his crappy Saves.
I know this may not satisfy everyone, but it's a way for giving importance to Luck and avoiding its reckless burning. You burn luck to hit a foe, you have a debt with Fate. Next time you'll need to be lucky, maybe you won't be (ie:failing that first "LUCK save", despite your great Saves, and getting petrified by Medusa).
Thanks everyone for the positive feedback on , well i should say "our" interpretation of luck.
I completely agree with Meinvt examples.