It depends on the person. My first LCD had 2 dead pixels, quite noticeable, but they never bothered me. Having said that, many companies actually have stated policies more like the 8-10 range, which is ridiculous. Unfortunately, the American public ain't too interested in demanding changes from them. Samsung has a zero defect policy in South Korea because competition is fierce there (the world's top two LCD manufacturers, Samsung and LG.Philips, are based in South Korea). Samsung also has a zero defect policy in Taiwan, because competition is fierce as well (the world's next two LCD manufacturers, AU Optronics and Chi Mei Optoelectronics, are based in Taiwan). But what is Samsung's stated policy in America? Ten dead pixels. That's right, ten. But American customers buy them anyway.
Last I checked, Hyundai Imagequest's official policy is ten dead pixels (for 19-inch monitors) as well. I don't see anything special about the L90D on their website, but maybe they come with an extra warranty card or something. Shouldn't be surprising, since I believe Hyundai uses Samsung panels; both are from South Korea.
As for what's acceptable, it really depends on the price you're willing to pay. If everyone were willing to pay around $450 for the el cheapo 19" LCD monitors (that would mean say $600-700 for brand name ones), then we'd already have monitors with no dead pixels. The market, though, is willing to allow some dead pixels in return for a much lower price. But most companies (include brand-name ones) stated around 7 or more for replacement; it's a rarity for a company to officially state that they will replace for 5 or less. Dell's official policy is 7 or more needed for replacement, but they make up for it with their 21-day return thingy.
http://erms.samsungusa.com/customer/sea...1&AT_ID=5608&PROD_SUB_ID=28&PROD_ID=-1
http://www.hyundaiq.com/cus05.asp