Dominion is designed to take 20-30 minutes, which is one of the reasons I enjoy it so much. However, I find that the card Saboteur causes the game to take much longer if more than 1 or two are purchased (which they almost always are) simply because it's nothing more than reverse progression.
All the other attack cards have at least some benefit to you, this just seems to be reverse progress, with no upside to the player. The only exception to this would be Sea Hag, however Sea Hag has a much smaller (and much less aggravating) effect on the flow of the game.
Besides "it's a good attack", are there any reasons to actually use Saboteur?