it would probably imply that the girl isn't confident in her legs. I think that's the only thing I'd really get out of it. There's really no huge change in how I see a girl just because she does or doesn't wear dresses. Sure, it's nice to have a girl who will show off her legs, but girls underestimate how hot well fitted dress pants look on them.
I wouldn't think much of it, we would at least notice though, if that's what you're asking. Since you don't wear them regularly. I'm not going to deny it though, when do guys not notice a girl wearing a skirt!?! =) To the random Joe he's just going to notice, but if you're trying to get a certain guys attention, then mission accomplished. =)
Well, though skirts and dresses are 'femenine' and show off the legs, they tend to hide the natural curve of the hips and thighs, while tight-ish pants emphasize these curves. However, I think that women who wear baggy guy-style pants can look just as attractive as women wearing tight pants, dresses, or skirts.
I know you are asking the guys, but I HAVE to add this! I think all girls look beautiful in skirts and dresses! I have known many girls who have never ever worn anything but jeans, and once in awhile they'd wear a skirt and its like an amazing transformation. Nowadays when I see girls who rarely wear skirts, I wish I could help them out by telling them they would look super good, but I'm a million percent straight so, unless they are a good friend, I wouldn't do that haha.