The latest statement suggests that some software will not work due to particular features and restrictions.
A recent statement from Nintendo suggests that some Nintendo 3DS software titles may not work on consoles from another region due to languages, age rating, parental control functionality, local laws in each area, and network services. Nintendo has said that to provide the best gaming experience, the possibility exists for some software not functioning properly when used on hardware from another region.
While this doesn't so far necessarily mean a blanket policy where all titles will not be playable out of region, it does seem that some titles will indeed be region locked. The 3DS will be released in three variations, for Japan, North America, and Europe/Australia. The statement finishes with the fact that hardware and software packaging will be marked with guidance for regional compatibility.
Previous reports from Japan indicated the implementation of region locking, with an e-mail support newsletter saying that software purchased in Japan will only be playable on Japanese 3DS consoles.
More exact details are expected at tomorrow's 3DS preview events, with a live stream for the EU event on Nintendo of Europe's website.