Saboteur is really only effective when you can hit your opponent's cards as fast or faster than he can replace them. The obvious way to accomplish this is with a strong engine (*cough* king's court), but if there is a lack of +buys, or if key cards are irreplaceable, like cities or minions once the pile has run out, one saboteur played frequently is still pretty strong. You probably want to slow down the game as much as possible since the damage you do is cumulative and meanwhile you'll be lagging in buying power (every sab in hand could've been at worst a silver. King's court sab? you probably could've king's courted a terminal silver for $6).
Here are a few games I dug up from my history (Sorry, I cherrypicked games where I win. They're the ones where I clearly understood what was going on and wasn't just experimenting/screwing around):
Here's a colony game where my scrying pool/festival/saboteur deck causes my opponent playing BM + mine to ragequit. I think scrying pool is something of a saboteur enabler because a) having saboteurs in a scrying pool deck doesn't hurt your buying power so much since you draw them "for free," and b) scrying pool gives you some control over what cards you sabotage. Silver on top? Discard it, since trashing silver isn't a big deal. Province on top? Leave it there and destroy it.
http://councilroom.com/game?game_id=game-20120610-052035-3a8bcf46.htmlIn this game I have some bad luck with YW bane and lose the city split 4-6, but with my better trashing and a single saboteur, I knock out four of my opponent's cities.
http://councilroom.com/game?game_id=game-20120613-214232-35514452.htmlHere's an old game I don't really remember and probably didn't play very well, but it looks like a decent example of saboteur as a desperation tactic. I get the dreaded and highly improbable single copper-potion-3 estate hand on turn three of a university/golem game. I'm behind most of the game, but among other things, I hit two colonies and a province with the saboteurs.
http://councilroom.com/game?game_id=game-20120316-114326-d71f79f0.htmlIn this game my opponent (an excellent player, by the way) plays a throne room/stables/smithy/hamlet/saboteur engine against my simple BM + smithy/apprentice deck. He hits me hard, four times per turn for a few turns, but some late-gained lighthouses and the apprenticing of my provinces let me run out the province pile before he can totally destroy my deck. I think his strategy would've been devastating had it not been for the endgame acceleration apprentice provided.
http://councilroom.com/game?game_id=game-20120619-124650-eb76ce05.html