Here's the low-down on the Longoria and Scott homers.
  The Longoria homer was indeed unusual in that it reached the second deck in left field, but that in itself doesn't necessarily mean anything in terms of distance.  My distance numbers are all derived exactly the same way:
1.  Determine the landing spot: how far from home plate did the ball land, horizontally, and vertically.  In this case, for Longoria, it was 392 feet horizontally and 40 feet above field level.
2.  Determine the time of flight of the ball.  For Longoria, this was 4.98 seconds.
3.  Determine the weather conditions.  This one is easy, 72 degrees and no wind.
With this information, Hit Tracker recreates the full trajectory of the ball, and from that it figures out where the ball would have been (i.e. how far from home plate) when it flew back down to field level.  That's the distance.
It turns out that Longoria's homer was somewhat less than what most people expected for precisely the same reason that home runs to the second deck at the Trop are rare: to get the ball that high in the air, that far from home plate, requires a very high-angled trajectory which is less than optimal for distance.  His ball came off the bat at 31 degrees, much higher than the optimal 27-28 degrees.  If he had hit the ball the same speed, but at 27 degrees, it would have gone farther, but not reached the second deck.

One other thing: long, high fly balls pulled straight down the lines are rare.  It is much more common for pulled balls (especially balls pulled right down the line like this one) to be lower trajectory, line drives, while for balls pushed to the opposite field, high fly balls are more common.  That's why Longoria's homer was unusual, and that's why second deck homers at the Trop are rare: the second deck is closest to home plate right down the line, but that is the direction that it is most difficult to hit one that is high enough and hard enough to get there...
Anyway, take a look at the two attached plots, this should illustrate nicely the short distance to the second deck down the line, and the much longer distance to the place Scott's homer came down...
I'd be interested to hear from whoever came up with 473 feet - I'd guess that their method would be a little less rigorous, but I'll give the benefit of the doubt...

Greg Rybarczyk Hit Tracker

 

As you guys can see, Greg was kind enough to take time out of his busy day to break everything down for us.  Here's the pics of each trajectory:

via i273.photobucket.com

via i273.photobucket.com

Here's a picture showing that it's not really as far as you would think to those seats, it's just the trajectory that makes it rare to get it up there:

062709_Tampa_Tropicana_Upperdeck5 (via baseballoogie)

And lastly, a profile of the expected trajectory, each red dot is a one second interval with green showing impact and the hypothetical downward trajectory:

via i273.photobucket.com