Goodbye, "Guiding Light." Hello, YouTube. Procter & Gamble Co., whose sponsorship and production of daytime TV dramas helped coin the term "soap operas," has pulled the plug after 77 years. Instead, the maker of Tide detergent, Ivory soap and Olay skincare is following customers online with a big push on YouTube, Twitter and Facebook. "The digital media has pretty much exploded," marketing chief Marc Pritchard said in an interview. "It's become integrated with how we operate, it's become part of the way we do marketing." The last P&G-produced soap opera, "As The World Turns," went off the air in September....