The iPad doesn't run Flash. If your website uses Flash, it won't play well on the iPad. Turns out, a lot of people want their sites to look pretty on the iPad. So the internet's already starting to look different.
One of the more interesting effects of the iPhone was that it drove a ton of websites to format their content for the phone in at least of two ways, and often both: iPhone-optimized sites, with more finger-friendly navigational elements that look almost app-like, and actual iPhone apps. We're seeing a repeat with the iPad, though the adjustment appears to be less about the screen size than its lack of Flash support, and there's the fact a lot of sites will be ready on day one. (Though before we go any further, let's be clear: Flash is sticking around, for many reasons, regardless of Apple's opinion of it.)