It recently went from June 29th to March 16th (see poster above) but has now been pushed back a couple of weeks to March 30. (I guess they'll have to have another print run of all the promo material.) This means there will now be 9 weeks between it and Snow White and the Huntsman instead of the previous 11.
From IBN Live:
Both studios are betting that the audiences won't overlap. After Relativity cut the gap, Universal did not immediately change its planned June 1 release.
Most movies make the majority of their ticket sales in the first few weeks after they debut. Still, Hollywood is betting the quick turnaround won't turn off people who might want to see both movies.
Relativity said the date change puts 'Mirror Mirror' within a week of the potentially lucrative Easter weekend. The studio also said the change made sense given a recent reshuffling of other movies, such as 'The Raven', which will now come out on April 27 instead of March 9.
As J.R.D.S. commented recently, a widget calendar with movie and book release updates would indeed be extremely handy with both the volume of fairy tale products and all the shuffling happening inbetween!