Piety

I get that praising a deity, offering them sacrifices and so on increases piety. I also know how to view a characters piety level yet i'm left with a question.

What is the piety scale? How high does it go? Is it most important for clerics or does it effect everyone equally?

Piety affects everyone more or less equally.

Clerics have to worry about their alignment more than anything. (RP is always nice, but not enforced)

I do not believe there is a limit to Piety. Crideas has his piety somewhere up around 1500...

There are significant thresholds for piety that will affect some things... such as how much % of your lost XP your deity might or might not refund when you step on the dais in the Great Hall after dying. I wont give you hard and fast numbers... but keep an eye on your piety level and pay attention to things like what I mentioned about XP refunds. You will eventually notice what levels seem to return what results... though I believe there is still a bit of random chance involved.

Piety can also be used to ask your patron for aid at their altars. I've only used it a couple times, and I'm not sure if different gods give different boosts... so far I've seen big stat boosts for asking for aid.

I don't know if this is a part of the piety question, but I know that on a few occasions when Sta'stillen was spattered all over the pavement, she was granted Lysis' favor and was returned to life with 1 hp. Not sure if that ties into piety or not, but there you go ...

That I believe is the favor of Lysis, much like followers of Dalix get a few bonus deflection AC now and then, and Gort followers get to do transferance now and then.

Lucky for many, the spontaneous deity favors aren't based on your piety score.