Will the iPad be excellent? I suspect it will.
Will I pre-order one as soon as it's available? Absolutely.
Will it become my most used Apple device out of my MacBook Air, Macbook Pro, iMac, Mac Mini, & iPhone? Almost certainly.
Will it offer a better experience than my BeoSound 5 for listening to music in my home? Absolutely not.
The reason is not so much the iPad, but rather the inherent strength of the BeoSound 5 and the inherent weakness of the AppleTV.
On-Board Storage: You can't appreciate this until you involve streaming into your home AV setup. At best it's mildly annoying. At worst it means consistent drop-outs in sound and intermittent freezing of software while connections are broken and re-established. It also means that your wireless network runs faster and your computer's processing resources aren't allocated to helping your home AV setup. And what if you don't want your computer turned on? So if you want a robust and trouble-free user experience, the AppleTV is not a serious choice.
Sound Quality: Even if you're willing to deal with streaming and its many problems, you'll never begin to approach the sound quality produced by the BeoSound 5. The sound-card hardware and decompression algorithms are stellar. If you're serious about sound quality (and presumably anyone spending B&O money is) you'd never consider AppleTV or other flimsy AV boxes.
Music Discovery: Apple genius is pretty clever, but it limitations are clear: if music has not been listened to or rated, it is not likely to figure into your playlists. It's great for mixing some of your familiar music, but not for discovering new music within your collection. Nor, in my direct experience, is the result nearly as enjoyable. So if you have a large collection and want to get the most out of your investment, the AppleTV will never be a serious consideration.
Interface: Unless you're thrilled with scrolling through lists, virtual keyboards, and distant video screens; you'll undoubtedly find the AppleTV a daunting chore to operate. The BeoSound 5's elegant interface is joyful and inviting and can navigate large collections better than any interface out there. If you have 300 CDs it will be remarkable. If you have, like me, over 1,100, it will be indispensable. So if you want to be able to access your large collection quickly and precisely, the BeoSound 5 is the very best choice.
All in all the AppleTV, iPad, iPod, etc. are novel media devices and most of us BeoSound 5 owners will undoubtedly have at least 2 of the 3 in our arsenal, but they will never be able to take the place of higher quality experiences like the BeoSound 5.