Not really, only when you first put it on. They're pretty hard to notice unless you're wearing the wrong size, or if someone yanks it out of the back of your pants and gets it wedged up in there. =P It's the same as any kind of underwear though. You don't really consciously notice them unless they're doing something they shouldn't be.
Man, I select the most random set of questions to answer.
Anyway, yes, I can feel it, and I never really get entirely acclimated to it. I feel like I have a slight wedgie all day. I personally don't like wearing a thong during, erm, intimate activities, because the weird feeling of the thong distracts me from, uh, other sensations. :P
Wow I think you are really into thongs. I think the other question was asked by you as well. Now off to answering your question.
When you first put it on, yes you can feel it, it's like any piece of clothing, you feel the fabric when you are first exposed to it. But as time goes by, your skin become habituated to the sensation and therefore you stop feeling it. Think of your socks, when you first put them on, you are very conscious, but as the day progresses are you really aware of them?