Many manufacturers put a dry clean only label on the garment because they want to save their own necks. Most polyesters can be laundered but if you are unsure ask a trusted dry cleaner for an opinion. To keep the newness of any garment it's always better to dry clean but for many items laundering is generally better than dry cleaning. For example if you purchase a polyester baby quilt you'd be better to launder it than dry clean but if your jacket is polyester it will retain its crisp new appearance with dry cleaning.

I found this at howstuffworks.com: Polyester fabrics are strong, resilient, wrinkle-resistant, colorfast, crisp, and hold pleats and creases well. But they are also nonabsorbent, attract and hold oil stains, may pill when rubbed, and may yellow with age. Polyester is used for clothing and filling garments and coats; some bed linens and towels are also made from polyester blends. Polyester can be safely dry-cleaned or machine-washed. * Turn polyester-knit garments inside out before washing to prevent snags. * Machine-wash polyester in warm water, using an all-purpose detergent. Use a chlorine bleach if necessary. Fabric softener will reduce static electricity. * White polyester fabric will look even whiter if you soak it overnight in a mixture of 1/2 cup automatic dishwashing detergent and 1 gallon warm water. Launder as usual, but add 1/2 cup vinegar to the final rinse. * Tumble-dry at a low temperature setting. Do not overly dry polyester; this will cause gradual shrinkage. * Press polyester fabrics at a moderate temperature setting, or use steam. In summation: dry cleaning may remove oil stains and will also not snag your clothing or polyester garments. Since polyester is non-absorbant, laundering at home may not clean the garment as well as dry-cleaning. I also made the mistake of putting a polyester blouse in a dryer that was set too warm and the blouse had permanent wrinkles from that point on. That wouldn't have happened if I had dry-cleaned it. When in doubt - follow the manufacturer's label.