We received an iPad Air last week and can confirm that there are no known issues with the FormConnect or FormConnect Pro apps. The only thing that was noticeable was that larger files imported more quickly than on older iPads (iPad 1, iPad 2, iPad 3, etc.). The faster processor made a significant difference.
The lighter weight of the iPad Air also made it easier to hold for longer periods of time which made filling out a form a pleasure. The narrower bezel also enables you to hold the tablet in one hand while in portrait mode, which would have been difficult to do with the older iPad models.