Some characters (*|/\:"<>?) are not allowed in group and note names.
This is presumably to prevent problems caused by using those names as names for the corresponding files where the notes are stored.

This restriction is annoying, possibly confusing, and unnecessary. Why should the name I am allowed give to a note or group depend on the idiosyncrasies of the target os file system's naming conventions?

Suggestion:

To keep the file/folder names recognizable, why not encode those characters in hex, in a way similar to url encoding? For example: "Is this good?" => "Is this good%3F", "a/b" => "a%2Fb".

Also, ".." should be encoded (see bug 9342), perhaps as ".%2E"?

p.s. I'd be just as happy if the file names were random numbers, as long as the mapping from note/group names to file names was stored in an easily accessable and well documented file format (xml file, sqlite db, etc.).