Smash Bros. for 3DS and Tales of Xillia 2 are all I have pre-ordered at the moment.

I generally don't, either, but in the case of Destiny and Forza Horizon 2, it costs me nothing extra to pre-order, and I get free in-game stuff (Destiny gets the upgrade Sparrow and Vanguard equipment, Forza Horizon 2 gets a Gallardo and 3 other cars) as a pre-order bonus.

I really don't complain about free stuff.  I'm probably the only person who didn't complain about the Club Nintendo rewards this year, because it's free stuff. They owe me nothing if they so choose.

at the moment, None for me. I had hyrule warriors pre-ordered but cancelled that after heaqring about the lack of online yet again for Nintendo. I also had destiny pre-ordered and then cancelled that after watching people stream it. Doesn't seem like a game that I would really play enough to justify spending $70 on. And I had smash bros. U pre-ordered but cancelled that due to the lack of News for it and the fact that it seems to be getting nothing compared to the 3DS version as the 3DS version has everything the Wii U version has and the Wii U has nothing really for it.. though I may re-pre-order it if they actually give more info about it.

Destiny
Middle-earth: Shadow of Mordor
Dragon Age: Inquisition

Not sure about The Evil Within and Alien: Isolation yet.

I am right there with ya on the Club Nintendo rewards.  Hell, I was actually excited and picked up NES Remix

None because I'm all digital now and digital pre-orders are not yet available on Xbox One! (but it is coming soon!)

What's the purpose of pre-ordering games though?

Halo: Master Chief Collection
The Order 1886 Premium Edition
Super Smash Bros
Halo 5: Guardians
Sunset Overdrive
Uncharted 4

Pre-order bonuses and you get to be one of the first people to play it. Those are the only reasons I can think of. 

It all boils down to how much you want the pre-order bonus. If you don't then you might as well just buy it release day.