HP's Slate computer, while still not available, is the closest thing to market so far that could be pitted head to head against the iPad. Despite some bumps for early adopters, though, the iPad has the potential to be mighty successful, especially with a new smaller version already in the works and a large ecosystem of apps and developers who cut their teeth on the enormously successful iPhone. The Slate? It looks like it will have some compelling features, but it's still very unclear as use cases emerge for tablet-like devices who will come out ahead. My bet, however, is on the iPad, given that iPod has now become synonymous with MP3 player and the iPhone remains the smartphone to beat.
There just happens to be one platform that is giving the iPhone a run for its money and is also slated for inclusion on a number of upcoming tablets: Android. Perhaps the use of Android on the Dell Mini 5 is the best indicator of its potential in this market. Dell, after all, has a penchant for letting other companies innovate and then sweeping into a market and finding real success with aggressive pricing and corporate features.
Android also gives us the best chance to compare apples to apples (no pun intended). Like the iPhone OS, it runs on ARM processors, integrates Apps functionality, and has quite a large user base in the smartphone market. Devices like the Slate run Windows, Atom processors, etc., making them more like netbooks without keyboards instead of purpose-built mobile computing devices.
Android, as in the smartphone market, has the potential to compete very seriously in the tablet market with the iPad because of the sheer number of device makers who can adopt and customize the open source platform. If you want an Apple tablet, you're buying an iPad. If you want an Android tablet, you'll be able to get it on everything from a Dell to an Archos to a WePad.
Will the HP Slate take off? Maybe, or it may be the harbinger of cool Windows 7-things-to-come, but I'm inclined to believe that as Android matures and penetrates new mobile devices spaces, Windows-based devices will become far less relevant. Windows may rule on the desktop for some time to come, but in the mobile market, it's an Android-Apple horse race (or at least it will be soon).