I usually play more carefully against a skinned champion, its a fact, maybe because normally people buy the skins for those champions they play with more often and therefore are better at playing them. Of course this isn't always true, sometimes, after a couple of minutes into a game I realize that the player who owns the skinned champion is probably a rich kid who has the money but lacks the skill. Since I do not own any skins other than the free ones, I believe I don't cause any "skintimidation" to anybody.
When I first started playing I used to see skins as kind of like a mark of mastery, if I met someone with a skin then they were obviously proficient with the champion. I don't hold people with skins to such high standards anymore though. Money doesn't always equal skill.
I always look at skins on less played champs, like Rumble or Shaco. If I see a Shaco on my team and he doesn't have a skin, I just assume he will feed. But if he has one, I assume he will at least put up a fight before feeding.
usually i assume that someone with a skin has played at least a few games with that champ....but i always find it wise to feel out your lane opponent for a minute or so before diving headfirst into a duel whether they have a skin or not, so it doesnt really affect how i play
that being said, i dread going into a game and finding like a poppy with a skin. you KNOW that nobody with a poppy skin is playing their first game with them, and in normals that usually means your top is going to get %$^%# up.