The regexp you are looking for is:

for which japhy's YAPE::Regexp-Explain] gives the following explanation (reformated):

The regular expression:

  /\w+ing\b/

matches as follows:
 
NODE                   EXPLANATION
====                   ===========
  \w+                    word characters (a-z, A-Z, 0-9, _) (1 or
                         more times)
   ing                   'ing'
   \b                     the boundary between a word char (\w) and
                         something that is not a word char
[download]

If you want strings like f***ing to be replaced use \S (matches anything but a space) instead of \W.

Your regexp does not compile, I guess you wanted to write something like /\S+ing/ which matches anything that's not spaces then ing but then strings like derringer (ing in the middle of the string) would be matched.