Originally Posted by
romat
A few years back I attended a seminar given by Dr. Ken Nordberg, a noted whitetail biologist. He feels that Deer have learned to look up, as deer hunting from elevated stands has become the normal in the last half decade. He said that his hunting success has gone up since he started hunting from the ground again, from pop-up blinds and brushed-in blinds. I currently guide in North Texas, here we hunt from ground blinds a lot. I like the versatility of a GOOD pop-up ground blind, can hunt any wind, wooded area as well as wide open fields. There is a time and place for each type, elevated or ground. The ground blinds are a lot safer.
+1
I know this for a fact, as I've had it happen to me. I was bowhunting in the George Washington Nat'l Forest in Virginia two seasons ago. I was in my Summit Viper climber and was covered head to toe in Realtree camo, including a facemask. I grunted in a nice 6 pointer to 25 yards.
Now, I swear to you right here and now, as God as my witness... that 6 pointer stood there and then
looked right up at me in the tree! 
I freaked out and closed my eyes, because I figured I was busted and it was all over with. (besides, I've heard that deer have that 6th sense, and know when something is looking at them, and they can see your eyes too). Thankfully the buck lowered his head and nibbled on an acorn and I quickly went to full draw and got him with an arrow.
Long story short...
DON'T think that you can't be seen in a treestand. Deer can and will look up at you!