Watchdogs stuttered with SLI on or off for me, didn't make any difference. SLI worked in the sense it scaled but it didn't fix the problems with the game.
Shadow of Mordor requires a change to AFR 2 and SLI then works, there might not be a profile yet but its simple enough to do that.
Titanfall didn't have SLI for me in beta, that combined with the frame cap and the lacklustre gameplay is why I didn't buy it, but i think they have fixed all these concerns now other than of course the gameplay.
You can probably add the latest F1 game to that list of not working as well, all the previous ones didn't support it, I doubt this one suddenly does.
I always say the same thing about SLI, there is always going to be a few games every year that you play on launch that don't have SLI support, its going to happen. So when you buy it you need to be aware of that and be happy with having just 1 card in that circumstance. Its never going to be the next BF/COD game, its going to mostly be a console port (Shadows of Mordor) or something where it doesn't make much difference due to really low graphics expectations anyway (Sims 4), but it will happen. Doesn't make SLI worthless, it just means its not a 100% solution.
For me at least 680 SLI has solved all the microstutter issues I had with 7970 crossfire. Gsync however really smoothed up the gameplay in a lot of problem games, like far cry 3. The game stutters but because gsync displays the frames at the right time its suddenly nice and smooth all of a sudden. From the data on pcper.com it looks like both SLI and crossfire have shaken off most of the extra variance and are well within tolerance levels (below perception). But without a doubt gsync is what makes SLI awesome because what stutter might remain is fixed by moving away from the fixed cadence of vsync. It doesn't matter if the GPUs are stuttering because the monitor just shows it at the right moment.
I have been using crossfire and SLI now for 5 years, its not all tea and biscuits but aside from one bad purchase its been better than having a single card. Where you really need that performance, like in the latest Crysis or Battlefield or any big graphics game you will have both working well out of the box. The companies that have SLI/xfire matter for them are the ones that ensure the profiles and game support are their from the outset. In the end that I feel is what matters its there on the games that really need it every time.