Update; I had two notes open on crash; cursor focus was in one, and that one disappeared from the notes list and ended up with 0 bytes in the share/tomboy folder, timestamped with the time of the crash. the second one disappeared at first from the notes title list, but I could find it by searching for words in it, after which it reappeared in the title list (and remained there through successive power cycles).
Update; I had two notes open on crash; cursor focus was in one, and that one disappeared from the notes list and ended up with 0 bytes in the share/tomboy folder, timestamped with the time of the crash. the second one disappeared at first from the notes title list, but I could find it by searching for words in it, after which it reappeared in the title list (and remained there through successive power cycles).