I don't believe the 50% number at all and I'm on my 4th Tour. It was a limited batch of Mexican assembled devices, because the plant was supplied with faulty components. Verizon addressed this very specifically in a recent release. Be careful about believing analysts - they don't have all the info and make wild guesses to get attention and make a name for themselves. When they're young, they get forgiven for being young and stupid...
I bought on day 1 of the release (received it on day 2) and had horrible trackball movement. I replaced it myself with the part from cnn.cn and am pleased to report it's functioning at 100%. Plus now I'm sporting a spiffy orange trackball! I definitely believe the 50% return rate. If anything I would think it's even higher. My local Sprint store got a ziplock bag full of replacement trackballs so they're obviously anticipating tons of complaints/repairs.
Picked me and my wife's up at the end of August and neither of us have the trackball issues. Hers has been perfect in every way. I am going through some annoying charging issues but other than that it has been great.
I believe they have whatever was wrong under control.