A YouTube user has done 2 comparisons between footage from the demo versus and the finalized version that was released last week. The footage doesn’t contain any spoilers if you already played/view the April 2009 demo version. You can notice some subtle differences like more detailed hair textures and improved lightning effects (lightning, not Lightning, okay?)
You can view them, as usual in HD, below:
Don’t YouTube too much for FFXIII videos because some people are stupid enough to put spoilers in the titles or descriptions.