As a designer I definitely get asked the most about paint, colors and finishes...why certain colors need to have a certain finish. So I have chose today to hook you guys up with a little info..and found it nicely put!

Flat paint finishes absorb light, they don’t reflect it. This particular paint finish is great for hiding any surface imperfections and looks good in most colors. The best rooms to use a flat finish is in spaces that receive little traffic such as bedrooms or closets. Keep in mind that flat paint is difficult to clean so try not to use flat paint in rooms that will require a lot of cleaning.
An eggshell paint has about as much sheen as an actual eggshell. It is similar to flat but offers a bit of luster and looks good in most colors. It is easier to clean than flat paint so it is ok for use in areas of your home that receive more traffic such as a hallway or a living room.
A satin paint finish is much easier to clean than both the flat and eggshell paint finishes.  However, don’t scrub too hard when cleaning because you could possibly remove some of the sheen which will leave an uneven finish in your wall. A satin finish doesn’t hide surface imperfections well, but the ease of cleaning makes it a good choice for spaces where walls may get dirty, like a kids room, kitchen or bathroom.
Semi gloss paints are a step up on the luster scale from satin as they reflect more light. It is a good choice for painting trim but could be used for a kitchen or bathroom because it doesn’t absorb kitchen grease or bathroom condensations as much as the other paint finishes do. Semi gloss paints generally look better in a lighter shade of paint.
Gloss paints offer the most sheen of all of the other paint finishes and is the easiest to clean. Gloss paint is generally used for painting trim and is usually not a good choice for walls. Gloss paint is also commonly used to paint cabinetry in kitchens and bathrooms.
Remember, these are just guidelines and not hard an fast rules.  At the end of the day, choosing a paint finish is a matter of personal preference.