In its current form, the Apple TV won't follow in the world-altering footsteps of the iPod. With its simple setup, superb streaming, ease of use, and quality output, it's a great piece of gear, but it will have more-limited appeal than the iPod largely because of the nature of DRM (digital rights management) and video. Music is widely available in unprotected form, so consumers can easily convert their CDs into digital files that they can consume through a device such as the iPod. Conversely, video content is highly protected. It takes a measure of technical know-how and patience to convert a library of DVDs to a format compatible with the Apple TV. Add to this the fact that DVDs offer advantages the Apple TV doesn't--5.1 channel audio, higher resolution, and the kinds of extras that a movie purchase through the iTunes Store doesn't provide--and it's clear that the Apple TV isn't for everyone.
However, if you've been frustrated by having to watch movies on your computer (or just as frustrated downloading those movies to a 5G iPod and then plugging it into your TV), if you prefer to enjoy nearly all of your media files through your TV and AV gear rather than splitting time between the living room and the home office, or if you have more media files in your iTunes library than you do DVDs on your bookshelf, moving to the Apple TV makes sense. You'll certainly enjoy the quality of the experience. Ultimately, your decision will be based on whether you have enough computer-based media files--and a fast enough network--to justify the purchase.