Like almost everyone else has said, Shedinja is kinda useless and/or requires far too much effort to make it work. The only things I see it being any good for are, like Platinum said, walling some Ubers, or to troll noobs who don't know what Shedinja is and how Wonder Guard works.
So long as you use hold items to counter Shedinja's stats and give it the right moveset it's entirely useful. For instance so long as it has moves like Phantom Force or dig then it's HP is a non-issue against Pokemon that actually can hurt it.
I don't see how Phantom Force and Dig help it out. You can't avoid attacks forever with those moves. Faster pokes will kill it before it can use those, and slower pokes can juts live through the PF/Dig and kill it afterwards. A Sash would only keep it around for one more turn before it dies (or whatever happens to a zombie bug husk). And its not like Shedinja has the Attack to do anything useful in that time.