Pretty well! you aren't just tied to using steam either. so far it works with my whole pc, I navigated here with my 360 controller.

I can see the usefulness of the steam controller already. Cant wait for it to get here.

The streaming itself I tested over wifi with Mad Max as it probably has the worst input lag in the best conditions and it was perfectly playable. The only way I could tell I was streaming was a few sound hiccups ( very light) and a few micro-stutters. But being Mad Max I am not too worried. Guessing using a cable would 100% eliminate these small problems as well. I think they will release some improvements via patches too.

Any delays become unnoticeable within 5 minutes of playing your games.