Hi,
We are running a few Trimble Yuma 2 Windows 7 tablets (Atom N2600) with the same issue, but when tapping on a text field we get the option of having the Tablet PC Input Panel appear which operates perfectly with no lag whatsoever. It lays on top of the white ArcGIS Mobile keyboard.
Do a search in Windows for "Tablet PC Input Panel" to turn it on, there are quite a few options.
I don't think it is the speed of the processor, as the Windows one works fine, just poor compatibility from ESRI.