Jeff Pearlman's new book about Roger Clemens was excerpted on Deadspin, and includes a section on Mike Piazza and his alleged steroid use. Here's a quote from the book:
"There was nothing more obvious than Mike on steroids," says another major league veteran who played against Piazza for years. "Everyone talked about it, everyone knew it. Guys on my team, guys on the Mets. A lot of us came up playing against Mike, so we knew what he looked like back in the day. Frankly, he sucked on the field. Just sucked. After his body changed, he was entirely different. 'Power from nowhere,' we called it."
In Piazza's first two minor league seasons, 1989 and 1990, he hit .268/.318/.444 and .250/.281/.390. After a breakout 1991, in which he hit .277/.344/.540 as a 22-year old in A+ ball, Piazza went on a stretch of 11 seasons in which he didn't post an OPS under .900.