@array = sort { 0.5 <=> rand } @array;

I wouldn't recommend this. From sort:

The comparison function is required to behave. If it returns inconsistent results (sometimes saying $x[1] is less than $x[2] and sometimes saying the opposite, for example) the results are not well-defined.

One could argue about whether "well-defined" simply means that the sort order isn't well-defined, or whether it means that something might blow up, but "The comparison function is required to behave." is a pretty clear statement.

Update: I see ikegami beat me to it.