Determine if all decimal digits are unique
Golfscript, 8 7 characters:

{`..&amp;=}



` - stringify the argument
.. - clone twice
&amp; - intersect with itself (remove duplicates)
= - check for equality.


if the function needs to be named (10 9 characters):

{`..&amp;=}:a


if a program suffices (5 4 characters):

..&amp;=