The big drawback: The iPad doesn't support Adobe Flash, used by most Web sites to display video and animation. iPad users who visit a site that uses Flash will be greeted with error messages. Many sites that are entirely Flash-based, like Hulu.com and TV network sites, simply won't work on the device.
There are two exceptions: CBS and Disney have said they'll format some shows online just for the iPad. But don't expect a deluge of TV outlets to follow suit, since most are owned by cable companies that don't want to lose subscribers. (Steve Jobs is a Disney board member.)
Also, Apple's Safari is the only Web browser for the iPad. Another bummer: Safari on iPad won't allow for tabbed browsing, which lets users keep several sites open at once in the same window.