It's Phoebe Cates. She stopped acting in the mid 90s to focus on being a wife and mother (she's married to Kevin Kline). I could see why younger people wouldn't recognize her. She's most famous for Fast Times at Ridgemont High and the Gremlins movies. Anyway, I'll agree with mleahy, Kathleen Turner probably has the most radical transformation. She has really bad Rheumatoid arthritis and she started abusing alcohol trying to cope with it.
Claudia Wells from the first Back tot he future film was BAD! I hated that they replaced her in the 2nd film. Shue didn't do it for me. I guess she doesn't look that bad.
^ Ah, s***. Jenna Jameson looks like she took a hammer fist to the face from Tito Ortiz. I wouldn't be surprised if she has some drug problems...
Yeah plastic surgery, drugs, and gaining or LOSING big time weight usually are the main contributors for younger people having a quicker decline. Like Posh Spice...
Kristen Stewart seemed like she had potential to look hotter as she grew older, until she turned all emo.