i've really been paying attention to my line lately and really getting in touch with my lure and whats going on down there.
i use braided line so its pretty visible on the surface of the water.
i have found there are VERY distinct feelings for each thing your bait encounters underwater.
it is difficult to explain, but i will try to type what i feel. i experience all of this when im fishing weigtless, t-rigged plastics.
when im pulling it through weeds, it feels kinda crunchy. cant really explain it better than that, crunch. imagin pulling your figners through very tangly hair. kinda like that.
i can always tell when my lure is about to hit a piece of rock or wood because i can feel my line scraping over it. braid is very textured so i can feel my line against hard objects. i will feel the vibration from the line and then it will just stop and i know my bait has hit the piece of cover. then i just ease the bait over it and continue.
gravel feels like a bunch of constant teeny taps, while mud feels like constant stickyness, like something is dragging your lure.
the most important thing i have found out when im fishing plastics is that if i am moving my rod and i feel something that feels like a hit, 90% of the time its not a hit. its just me pulling the bait into/through something. however, if im not moving the rod or reel and i feel a tap or see my line move at all, it is a fish of some sort, and i'll let em have the bait for a few seconds, reel in the slack, and set the hook hard.
hope that helps you distinguish some stuff.
PS. dont worry about what the other guys say, just do what feels right to you.
good fishin!