Paul,
Personaly, I tend to look somewhare in the region of the mouth/nose area of my opponent, this is due to many of them being (at the time) Kyu grades, and I think that it's un-nerving enough for them to face a Dan-grade in Gohon Ippon, let alone being stared at as well.
For other partners/opponents, I tend to look them in the eyes, I feel this is a necessity, not just to 'see' their movements, but to gain control of the fight/situation.
I remember reading once an interview with the late Steve Cattle (WKSA and former KUGB team member) about this, he stated that he looked at his opponents chest, and I think his words were "as if there's a great big cross on their chest", he went on to state that he could anticipate his opponents attack, since they almost always started from this area of the body. I'm not sure if he meant that they 'telegraphed' their attacks, or if the inhalation of the opponent allowed him the split second timing to counter??
Anyway, I tried this, and it did'nt work for me, I think that it's up to the individual to find what works for them.
Dave Hooper Sempai always stresses that you should look into your opponents eyes, and comming from someone who's trained at taku-dai, I think maybe he's on to something.
BTW, the article with Steve Cattle was in one of the old Fighting Arts Int. magazines, not sure if any still exists, maybe 'KAMAE' (the gi people in Chester) may have some of the back issues left, if I have time (or bored one day) I'll go through my issues to find the No.
Mole Bach