What exactly does it do? I know it's supposed to show the path to the main goal (that you have selected), but I don't see any discernable effect from the spell. All I get is a small ball of light that surounds about 6 inches off hand. There's a stream that ALWAYS points to the upper right hand corner, regardless of where I am facing or what quest I've selected. As far as I can tell, it does absolutely nothing. What am I supposed to be looking for? Does it only work with 100 Illusion or something?

Yeah, unfortunately clairvoyance is completely bugged and what you describe is one of the common bugs, the path just doesnt show up at all.

Also fun, when it does work it will send you into a mountainside, floor or the door youre supposed to exit the dungeon from and that is locked from the other side with depressing regularity.

I had planned to play a Dunmer whos ancestors guided his path with that spell, but I had to give that idea up or accept that my ancestors do not like me.

I dont know, every day Im finding more dissapointments with Skyrim.
It seems I cannot find one single feature that is finished and debugged.

Make sure only you only have one quest active.

You have to hold down the “casting” button a few moments. If you don’t see a path, rotate your character and keep trying until you see the “path”. This spell doesn’t always show the quickest route, seems to prefer established paths and roads.

I haven’t had much problem (though I've never used inside) with the spell, except the tendency to take me on a ‘round-a-bout trip on occasion.

I haven't ever had problems with clairvoyance. I use it quite often. You have to hold it continuously and give it time to "paint a line" on the path. It even works for my custom map marker. Best to be standing still when you do it, although not necessary.

Clairvoyance works fine most of the time for me. It's really good to get you back out of a cave or dungeon quickly once you have cleared it

I almost always use it as I run. The line updates just fine. -shrug-

It works for me.
You need to release it
Also don't run around with over nine thousand quest markers.

The only problem i have is sometimes it takes me way out of the way or directs me to a far door when a closer door is better...use it along with your own judgement and it will guide you

Yes, only having one quest active is the key.

Casting it a lot will also gradually increase your illusion skill.

Make sure you only have one quest active as they say and also make sure that you do not have any markers in place. Removing a marker is a case of clicking somewhere else on the map and then selecting Remove it. Even doing all that it, shall we say, has its moments when it is not so much help. In corned rat it kept directing me through a solid wall, so in that instance I gave up on it and wandered around until I found the very security concious person I was looking for. One other tip like any other spell let it charge before use and watch your Magicka if you haven't been built that up.