Version 10.0.3 has a lot of features added that video nerds have been asking for since Apple revamped their Final Cut Pro software, but the biggest feature to me is the multicam functionality. Not because I have a ton of cameras to keep in sync on video projects, but because they've allowed for different types of video to be synced automagically for editing:
It does not end there. The biggest surprise is that unlike any other NLE, FCP X allows multicam projects to handle cameras with different codecs, image rasters, and frame rates, without conversion. Think about handling a multicam project that includes footage from DSLRs and DV, HDV, and professional cameras, without having to pre-process the content first. You can change, add, or delete camera angles at any time and work with different codecs, frame sizes, and frame rates without conversion.
So if I shoot video with my Canon HDV camera and have my iPhone 4 recording as a secondary shot, I'll be able to easily lineup and edit those two angles together without having to spend as much time re-encoding and lining up the clips.