are these 2 skills (and the alertness feat) of any use in the OC? or outside of OC for that matter?

Do they work against the invisibility spell too (or any spell that offers concealment) or only against the hide and move silently skills? Actually even if they did work against spells they still would seem ptetty useless.

They work against the Stealth skills, and Spot also helps you detect a pickpocket attempt on your person. Beyond that the skills only have as much use as module designers (and the players) give it.

It is not unheard of to have to roll a Spot or Listen check when you're out on a DMed quest for example, where good rolls give you a better idea of where the plot is going, help you find the better solution to a problem, or even provide that one final oppertunity to escape certain death. But for the most part, no, they're not the true must-have skills.

Well thanks Legolas. Guess that makes them pretty useless in the OC. I've never seen (no double meaning intended) anyone there use the stealth skills... nor try to pickpocket me...

They also help you see through invisibility. the mind devourer cast invisibility and i could still see it... how many ppl cast invis in the OC?

The invisibility spell 'fades' whenever you're up close to someone using it. I'm not sure what the thought behind that was, but it happens regardless of whether your detection skills are in the hundreds or the negatives.

yes... I think I saw something similar happen to some invisible creatures and I dont take any skill points in spot/listen. But I thought the 'fading' was because the monster would do some hostile action which would break the invisibility. could it not be because of that?

It could be, but only with an improved invisibility spell. A regular invisibility spell simply wears off when you perform a hostile action, but improved invisibility gives you a 50% concealment bonus. The semitransparent appearance is part of that concealment effect.

You are also told when you swing at something that is concealed... well, when you swing and miss anyways. So thats not it. Only possibilities i can think of are the invis fading as Legolas said, or my spot/listen skills showing me where they are.

OK just one more question. How are the spot/listen checks applied against stealth checks? Are these checked every round anew, or only once?

Every round