Kilometer

<<I've seen people write such things, and they just don't seem right to me at all - and it's not that the consonants themselves seem wrong, but rather that the vowels don't seem right if I actually try to read them aloud (thanks to vowel length).>>

They seem right to me, just spelled wrong. "shutter" and "shudder" as well as "grader" and "grater" are exact homophones for me, no length difference.

<<At least for me, "utter" and "udder" for instance have the same vowel length and are exact homophones.>>

To me they are different, and so are "shudder" and "shutter" and "grater" and grader." I haven't seen anyone get these confused when writing, either.

Maybe it's a regional thing. Does anyone know where the shutter/shudder merger is most common?

<<I think this came up a couple of months ago. In my accent, vowel length seems to be more dependent on tenseness than environment. 'Shutter' and 'shudder' are homophones as ["SV4@`]. With 'grater' and 'grader' I'm not as sure; I think there may be a slight difference.>>

The same is probably true for me.