The ipad may be (by the uninformed) a toy,however i am a recording engineer and have use the iPad to record guitars and I must say,that the app that I used to record with gave me the best recorded guitar sound that i have heard without miking so good in fact that other engineers in my area always ask me how I get my guitar sound,another thing to be aware of is that there are a couple of pro level DAWs for IPad that is not only endorsed by professionals but pro level software pluggin companies have jumped on the bandwagon,so you can see that the ipad can be a pro level recording and mixing solution if one so chooses and there is more that enough pro level i/o solutions to help facilitate that.
I totally agree with you, I use the iPad to create music and it gives me full satisfaction. Some apps are really Pro level and regarding hardware, this is only the beginning, so there will be even better controllers in the near future.
Can you tell us what apps you use ? The ones you like the most / the least ?