We hear cliches everyday but we rarely stop and wonder where they come from. For me, I try to avoid the cliches that I don't know what they really mean. Of course, the meanings are open to interpretation but there usually is a consensus. To try and find out their origins/meanings, I often turn to this site.
GoEnglish.com doesn't have every cliche I've wondered about ("oil and water" and "let it roll off your back like water on a duck" are just some of them), but it has plenty. I know a lot of this is "duh" for a lot of people, but for someone that wants to know specifics about these phrases, I seek clarity from more sources.
"Between a rock and a hard place" is one of those phrases I never really understood until recently. I kept having this visual of being stuck between rock formations on a beach and not having a way to get out. A rock is a hard place so what makes it sound like there is a difference between a rock and a hard place? I just say, "I'm stuck and don't know what to do" instead.
Then there is the one about having a "chip on your shoulder." After reading GoEnglish's explanation of it (To start a fight, men used to put chips of wood on their shoulder and challenge others to "try to knock it off"), I still don't understand. When was the last time you saw somebody with a piece of wood on his/her shoulder, egging people on to knock it off? I always thought that having a chip on your shoulder meant that you had a wound that never fully healed (or not at all) and you were still bitter about what caused that wound.
My point is this: if I don't understand a colloquialism, I try not to say it. There are just one too many phrases that come from a different time and approach. I'm not about to jump on someone's case if he/she uses one, but don't expect me to talk about setting bridges on fire, mixing oil with water or analyzing the the shades of greeness of someone else's grass.