I haven't seen anything official but since Paris is now out, I believe LA is the only logical venue for the debute if it really is going to see a 1st quarter release.
Also, some new spy pics hit earlier today. One really nice profile shot.
Even though hardely anyone else on this forums seems to care about the 2010 Mazda3, here are a couple more articles with some new info, a brief driving impression, and some spy pics of the hatch (finally!)