I wouldn’t even call one that just shows a leg outline to be see-through. But real see-through is worse, definitely.
Either one is less tacky that what I saw today, white shorts with dark underwear underneath, easily visible even inside.
I am going to come out as the voice of old-fashioned virtues and say you should never be wearing a skirt or dress without a slip, period. If the slip shows, either roll it at the waist or don’t wear the skirt until you can get a slip that fits properly. Yes, even lined skirts. They’re not built-in slips, they’re linings.
Get off my lawn. 
I would never wear a skirt without a slip. Not because of the leg outlines showing (although that would make me enormously self-conscious) but because the whole point of a skirt is the way it moves when you walk. And it can’t drape and sway properly without a smooth slip underneath; especially if you are walking outside and get the tiniest bit sweaty. In that case the skirt will begin to stick to your legs and ride up or twist in very uncomfortable ways.
ETA: Having read the reactions of the men in this thread, I now also fear that the legs showing might be taken as an invitation of sorts, or a statement of intent. . .
What’s really tacky is wearing underwear with a see through skirt. That’s just disappointing.
I think men and women will have a different take on this question.
Is a slip what we British call a petticoat?
Nylon–but silk slips really aren’t all that much more expensive.
A slip is a sort of underskirt. I think of a petticoat as being very frilly and adding fullness to a skirt, which a slip does not do. I don’t know the British usage.
We don’t do it on purpose (well, not always). Sometimes I’ll buy a skirt that’ll be quite thin, but have a built-in “slip” of sorts underneath, so it’ll look fine when I try it on. Then I’ll go out in public and find out that despite the layering, it’s STILL see-through. :mad:
As for the poll, eh, I can’t decide.
Sounds like this is not really a see-through skirt if it is only see-through when backlit by the sun. Just don’t wear black undies.
Visible slips are not appealing and often look bad with the skirt. e.g., shiny tan nylon under a colored cotton skirt.
Wait, you’re a woman? <d’oh>
Where do you shop? 
I did mean see-through when backed by the sun etc; not transparent all the time. What Maiira said basically.
I don’t ever want anything I wear to be see-through in any circumstances. Stop looking at me.