Did you know there is a new computation type in APEX - SQL Query (return colon separated value)? Probably not, because there are many other "sexier" features. However this "small" feature is realy cool. Before, you needed to do several steps if you wanted to compute your multiselect list, shuttle item, checkbox or a radio button:
1. DECLARE an array,
2. SELECT * BULK COLLECT INTO array
3. use APEX_UTIL package to convert that array into a string
4. RETURN that string
With APEX 4 you don't need to do that any more. You just do a normal select and whatever it returns will be concatenated into a colon delimited string. That's it.