Or actually what I hope to HEAR or READ about since I won't WATCH it :-) Though pro days are scripted events designed to showcase a QB's strengths and hide his weaknesses - which is why the media's gushing over Robert Griffin III's session is meaningless, as we already knew that he was accurate and had good arm strength - we fans can get some useful information from Luck's pro day.
Let's be honest: the only question about Luck is his elite arm strength. (Well, some SEC fans wonder about the quality of CBs and DEs that Luck faced in his college career, but let's just ignore that.) And elite arm strength is not measured by deep balls, i.e. "being able to throw it 60 yards in the air downfield." This excellent and brief piece talks about various routes, and here is a similar one. The routes that require superior arm strength: the hook and the deep out. (I will say that the medium post and comeback do also.) These require the ball to travel more than 15 yards in the air, but to areas of the field where there are defenders, and also across part of the field. This requires the ball to travel through multiple areas where it can be defended - as opposed to short passes which are generally thrown in front of the defense and vertical throws where it travels over their heads - and often to a WR or TE that is not "wide open." With these passes, the defenders will often see the ball coming and be in position to intercept the ball or at least bat it down. The only thing preventing it will be the velocity of the football. A quick release helps only a little bit, and quick reads even less because these routes are going to be part of the progressions for everybody but the "captain checkdown" types, and the better QBs can even be flushed out of the pocket (or move around in the pocket) and still complete these.
So when you watch Andrew Luck's pro day tomorrow, look for evidence that he can make those routes. Luck and the coach that is guiding him through the workout process know that everyone is asking these questions. If he throws several such passes - i.e. all the difficult routes such as those listed in those articles, and throws them several times - then no worries about his arm strength. But if he shows those routes short shrift tomorrow, then that will mean that Bruce Arians is going to have to build an offense for him that looks a lot more like what Drew Brees and Tom Brady do than what Peyton Manning did. (The folks who state "they questioned Manning's arm strength too" are off base. There was never any question about Manning's ability to make any NFL throw. For instance: Peyton Manning threw at the NFL combine. Which is an example of why those who claim that Luck is a better prospect than Manning was are simply wrong. Now Griffin III also didn't throw at the combine, but he was concerned about criticisms concerning his accuracy on certain routes, footwork and throwing motion, not arm strength. Which is why Merrill Hoge and other folks who claim that Griffin is a better prospect than Luck are also wrong.)
The issues that guys like Vince Young, Tim Tebow and Alex Smith were going to have at the NFL level were predicted by the routes that their handlers did not have them throw at their pro days. Of course, Luck is going to be much better than all of those guys, but based similarly on his pro day, we will be able to guess what the Colts' offense will emphasize and de-emphasize in the Luck era.