How about Android tablets? Or windows tablets? (I do realize, or at least I've never seen, that there is no multi-touch on Windows tablets), but touch screen is, and many of the drum/midi sound apps are available on windows tablets... and they are becoming available in smaller form factors, too... maybe not quite as small though...
Well.., uhm.., Android - I've got an Android smartphone two weeks ago and since then I was trying to find apps on The Market that are worth to download for my music purposes. Honestly said, I didn't find anything that is as easy to load, easy to configure, easy to use and functional like the apps I've mentioned on the iAny's.
Don't know if there are such Android apps but it isn't me who walks blindfolded I believe.
Yes, some of the Windows/Android tablets have much more horsepower and a doubled number of interfaces for more input but - as Steve Jobs mentioned today in his round-up - that's not what a tablet makes a hot gear. Simplicity, functionality, usability, smart design - that are my 4 Aces.
And no - I'm not a Jobs-aholic or Mac-fanboy
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I've been working with PCs, UNIX-workstations and Macs my whole life in parallel and won't miss this freedom of choice in future.