Susanoo-No-Mikoto is a hard sell for the corp. 9 to rez a piece of ice with only one subroutine? Why bother when Tollbooth, which costs 1 less, has more utility with a very taxing non-subroutine effect?
The answer lies in what SNM is supposed to do. And I'm convinced this is there to do one thing—to flatline the runner. Jinteki may have more ambush assets than you can shake a stick at, but it's usually impossible to steer a runner into them. Most runners will just avoid an archives with several face-down cards, especially if they see a deck with little ice and laden with traps. SNM, however, can force them into the spider's web, but has to be used carefully to get the intended effect.
The key to SNM is patience, along with its wording—"...until after he or she encounters a piece of ice." This means, if you have no rezzed ice on your archives, they must access archives! Or, you can drop some ice with net damage (e.g. Komainu, Cortex Lock, or even Neural Katana) with a nasty Whirlpool to ensnare runners without AI breakers. And, for the most part, SNM becomes more dangerous over time, as your archives fills up with Shock! or other ambush cards usable from archives. Lastly, putting an unrezzed Hokusai Grid on archives, or a House of Knives with counters available, provide other options for the final coup de grâce.
Rezzed at the wrong time, though, it may do nothing more than hurt your wallet. It's most effective with the element of surprise, before Femme Fatale can latch on and make it nothing more than a joke. Speaking of downsides, expose can throw a wrench in your plans, unless you have Zaibatsu Loyalty handy. And, there are several cards than can make SNM a liability, namely Forged Activation Orders. Finally, a usable Switchblade laughs in its face, Snitch can make it cry, and Faerie is found in more than a few decks and can easily limit available rez windows where it could otherwise do heavy damage. Oh, and how could I forget Hades Shard...
Even if the surprise factor is lost, a 7 strength sentry is nothing to sneeze at if the runner doesn't have a Femme or a usable Switchblade handy. And, while I don't see ever having three copies of this in a deck (and not just because it's unique), it sure is fun to drop a single one in a Jinteki deck every now and then—it might just win you the game.