Eli Zaretskii <eliz@gnu.org> writes:

>> The overhead disappears only if I comment out (narrow-to-region
>> (field-beginning) (field-end)) in
>> thing-at-point.

Are there fields in the buffer you're using this in?  I.e., does
(field-beginning) (field-end) return anything other than
point-min/point-max?

> Perhaps thing-at-point should acquire a new optional argument saying
> "don't pay attention to fields"?

If the buffer has fields, then I think thing-at-point should pay
attention to them -- it's for stuff like this Emacs has fields in the
first place.

--
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no