thanks all is very useful, Im looking at a POS system, and pre 8.1 (or build 2013 ) I was very concerned about using a windows surface device as we're looking at card reader, and interactions with a cash register (though usb) - I was thinking that this would only be possible on a surface running pro and not 'store' sandboxed apps... but it looks like with 8.1 it a go on the surface RT
other things to look at are storing and retrying processes if internet connection is lost etc.. so again there will be some questions around serializing a state of the app or possibly running an in memory 'lite' db (hey dictionary maybe) that can resume state even after a power down etc.
If a customer already has the surface pro or pro desktop then the app should run fine on this...
Jim what platform was your POS system? Is silverlight the xaml engine on windows phone 8 and is the xaml engine for windows store apps something else?