Slips were once considered a necessary undergarment, much like a bra or a pair of panties. At lunch today, a co-worker retold a shocking story about a teenager who came to school dressed in nothing other than a lacy slip (she claimed it was a "dress"). Someone coolly remarked, "She probably doesn't even know what a slip is." Another demanded, "Does anybody even wear a slip anymore?"
Oddly enough, I was wearing a slip under my Zac Posen cut-out skirt (it would be quite scandalous without one). It was not a slip I purchased separately, but one that came with my Prada lace skirt--one of the only "designer" pieces I own that came with a separate, detached slip. Other than a few sheer dresses, clothing today usually comes unlined and unslipped (to make up a word). Designers also have no problem sending a model down a runway with transparent clothing, a small detail that is excusable so long as a beautiful woman's assets are revealed.
The au courant thing is to wear Spanx, leggings, or opaque tights under a see-through or snug dress, but I prefer a standard nude silk slip under looser garments as a less restricting option. And while slips may seem old-fashioned and cumbersome to some, I enjoy the smoothness a silk slip provides as I sashay down the halls. At the very least, it removes the itchy chafing that comes from the absence of lining.