It's not a Spring 2010 trend anyone can wear...but should you decide to don the Romper (aka, a short jumpsuit)...a couple of tips.
1) To avoid looking childish or costume like, look for a Romper in a grown up neutral colour like black, navy, khaki, or grey. You can add colour later with your accessories.
2) Continuing with the whole "avoiding a childish look" theme...keep the style simple.So no ruffles, lace, or embellishments.
3) When it comes to fabric, something with some hold is best. Think built in bustiers, and stiffer fabrics. In other words, no terry, velvet, or jersey.