My video camera records onto a memory card which mounts in Ubuntu with no problem. I see a bunch of .mp4 files, but what software do I use now? I installed PiTiVi and repeatedly tried to import the folder of .mp4 files but it keeps crashing after importing a few of them. I tried running pitivi from the command line to see if it output any messages, but all I saw were errors about creating thumbnails and then "Segmentation fault". Now what?
That does sound like a bug in PiTiVi. You could try other video editing software like Avidemux or try to convert the video to a format more likely to work with OggConvert. Both are supposed to be able to handle mp4 files.