An unspectacular quarter and disappointing guidance from Yahoo! ( YHOO) took a heavy toll on both Internet search-engine stocks and the larger universe of speculative technology names. Yahoo! plunged $3.62, or 11.1%, to $28.98 in premarket trading Thursday after delivering second-quarter revenue about $2 million short of estimates and saying third-quarter revenue would be $610 million to $650 million, on the weak side of the First Call consensus of $646 million. Joining Yahoo! in the downdraft were the two stocks most closely associated with its post-bubble arc: Amazon.com ( AMZN) and eBay ( EBAY). Amazon, which was roughly flat for the year but up 25% from its early May low at the close of trading Wednesday, skidded $2.59, or 5.1%, to $48.41 in premarket action. eBay, which had risen 28% in the year to date, tanked $3.67, or 4.2%, to $83.20 in premarket action. Meanwhile, discount site Overstock.com ( OSTK) fell $1.86, or 4.8%, to $36.41 in after hours trading Wednesday. While all three stocks felt immediate pressure on Yahoo's guidance, the Internet sector was also the subject of negative research issued earlier in the day by Prudential Securities. Prudential downgraded eBay to neutral from overweight, citing its runup and the potential for demand problems over the summer. "As we head into the seasonally slower summer months when Internet usage and fundamental growth rates typically decelerate, we believe the sector could experience added volatility and downside risk," the brokerage said. Several search engines saw their shares slide, including Looksmart ( LOOK), Mamma.com ( MAMA), AskJeeves ( ASKJ), and FindWhat ( FWHT). Another casualty was the Web advertising space. Shares in Infospace ( INSP), DoubleClick ( DCLK), and tech-news site CNet ( CNET) all fell after the bell Wednesday.