Is it ever proper to use the phrase in between (as in "in between the
two cubicles" vs. "between the two cubicles")?

Hi baldbc,

Certainly there are cases where it is perfectly acceptable to use the
phrase "in between."  In some cases, "between" may be preferred as a
matter of style, but "in between" can certainly be grammatical.

"In between" connotes location in a space between two endpoints, so it
sounds more natural in some usages than others.  To use your example,
consider these two sentences.

1)  There was a rock on the floor in between the two cubicles.

2)  There was a partition in between the two cubicles.

To me, 1) sounds fine, while 2) sounds a little odd, though not ungrammatical.

In a Language Corner article for the Columbia Journalism Review, Evan
Jenkins discusses this issue briefly, but doesn't take any firm stand
on preferred usage, and doesn't mention anything about grammatical
incorrectness.

http://www.cjr.org/tools/lc/inupon.asp

The phrase "in between" appears in the The American HeritageŽ
Dictionary of the English Language (Fourth Edition, 2000), which
suggests that there are cases where it is proper to use it.

http://www.bartleby.com/61/59/I0075900.html

--efn

"In" is superfluous, regardless of grammar.

I don't think so

'between' can mean from A to B, eg: connecting A to B

'in between' generally means 'within the space between' 
- not necessarily 'connecting'

However that is from a UK English perspective.

I'm between a rock and a hard place.

I'm in between a rock and a hard place.

Which sounds right?