Just tried it on my ipad and iphone for a couple of minutes. Not a big fan of the remote section, as the touchpad feels loose and laggy to me. I have the original xbox remote (with my HD-DVD add on) and having the real remote is much better.
I haven't tried any typing yet, I have a chatpad, but to be fair I hardly plug it in. This may be a good use of the iPhone/iPad smartglass.
The big draw in my opinion will be the 2nd screen during gameplay, we will see how it is implemented. It could be just another useless add on, or it could be a great, the jury is still out.