I wrote a blog post about how the apparent PTR change to making raw Cata gems unable to be sold to the vendor may affect players who have an abnormally high stock of raw uncommon and rare Cata gems they may have been planning to vendor at some point.
My full post can be found here but the TLDR is if you don't want spend tons of time cutting and vendoring underpriced uncommon or rares in 4.3 it may be best to sell them now.
Why do you think Blizzard made this particular change?