Which current ballparks have hitters or pitchers an advantage?

I'm trying to find out how people feel. I've heard of "park adjusted" stats, especially for homefields, low fences, short distances to OF. Can someone explain to me how they affect a hitter's or pitcher's performance? The obvious about the distance to OF aren't what I was looking for. Just anything what may qualify as "significant" to kind of put an "asterisk*" next to a player's stats.

Let's hear it.