villian min bets, what does that signal?

[shutEMdown]

A min bet of say 40 into a 460 chip pot is so annoying and most of the time online it means weakness. I generally call the min bet on the flop with just about anything and then raise on the turn. occassionaly though villian will min bet the turn into a 600 chip pot, I make it 400 to play and he still calls. I mean, if you betting 40, what makes you think ur hand is good enough to call another 560? does anyone min bet into fairly decent size pots and if so, what does it accomplish?