Two characters shorter (64):

perl -pe "
 s#(\w)(\w+)(\w)#join$,,$1,sort({(-1,1)[rand 2]}split$,,$2),$3#ge"
#12345678 1 2345678 2 2345678 3 2345678 4 2345678 5 2345678 6 234
[download]

It should be possible to golf that down some more, but I'm late for bed. (: Have fun.

So all but first and last must be reordered, but nobody said they must be randomly scrambled. 35

perl -pe 's/(?<=\w)(\w+)(?=\w)/(reverse$1)/eg' file
          12345678901234567890123456789012345
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Ditch efficiency and save four strokes: :-)

    perl -pe 's/(?<=\w)\w+(?=\w)/reverse$&/eg' file
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--
John.

Doh! And I guess we don't need no stinking look(ahead|behind)s either (22):

perl -pe 's/\B\w+\B/reverse$&/eg' file
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Again, hmm, this one always gets the right letters on the ends as far as I can see, but doesn't necessarily mangle all words. I just got:

Aircnodcg to a researhecr at an Enigslh urisnviety, it doesn't matter in what order the ltertes in a wrod are.

in which quite a few words went unmangled.

---




($_='kkvvttuubbooppuuiiffssqqffssmmiibbddllffss')
 =~y~b-v~a-z~s;                             print
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Yes, your original spec (that my solution was written based on) had a requirement that "the rest of the letters must be out of order". I realized that this requirement was impossible so I chose to ignore it rather than implement an infinite loop (as you first did) or to ammend the rules in a different way (as you later did).

Personally, I much prefer having the order be random over some fixed reorordering that meets a "must be out of order" rule but doesn't meet the spirit of the original problem, IMHO. Both "must change if possible" and "random" would be best, but if I pick only one of those two, then "random" is the clear choice to me (though the other choice certainly makes for shorter code). :)

                - tye

How about this:

 perl -pe 
 's#\B\w+\B#join$,,sort({(-1,1)[rand 2]}split$,,$&)#ge'
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That's 52 chars without the "perl -pe"

perl -pe "s#\B\w+\B#join$,,so­rt{rand~0}split$,,$&#ge"
#         12345678 1 2345678 2 2345678 3 2345678 4 2
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                - tye

$str = '
According  to a researcher at an English university, it doesn\'t 
matter in what order the letters in a word are.';
$str =~ s/(\w)(\w+)/split"",$2;$,="";$,.=splice@_,rand@_,1while@_;$1.$
+,/eg;
print $str;
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I get "Anogdcric to a reecasrreh at an Enghsli uyirenvist, it dnseo't matter in wtha oderr teh leettrs in a wdor are."

Which doesn't fit the brief.

Some words are not mangled, and nearly all of them have the wrong last letter.

($_='kkvvttuubbooppuuiiffssqqffssmmiibbddllffss')
 =~y~b-v~a-z~s;                             print
[download]