It would be nice if, when a file changes out from under
NEdit, you had the option to merge in the differences,
like an interactive patch merge. Kind of like how
eclipse does its team sync stuff, if you've ever seen that.
You could do a side-by-side diff of some type, and show
each chunk separately, giving the option to accept or
reject each one, or to accept or reject all; then each
chunk could be one entry in the undo history, like a paste.
Coolest of all would be a 3-way diff, for if you've got
unsaved changes to a file, and the original working
file got updated externally. You could merge the diff
of original->new file into the working file.
Anyway, that beats either (a) throwing away all your
unsaved changes or at the very least (b) losing your
undo history, both of which kinda suck.