Well, here's my report:

We tried it last night.
One good thing we did was to relax a lot before - and to talk about all the day-to-day stuff first.
It was incredibly hard to concentrate on my breathing AND his, AND on his eye. These really are three different activities - even doing two of them at once was hard!
I kept wanting to let my gaze widen to take in the rest of his face - if I concentrated only on his iris, I felt like I was falling into a kind of trance, without really seeing anything.
There was one point at the end when I was following the instructions to look for "the universal man" in him. For a while, I imagined I was seeing him as a child, and then as an adolescent, but then I had this overwhelming urge to hold him and to talk to him, and we stopped, and just sat there in each other's arms for a long time.
No clue as to how long it lasted - between 3 and 10 minutes after we opened our eyes.
When we had sex later, there was more physical contact than usual - I mean, more pressing together.
Do you think it's ok to move around a little, if eye contact isn't broken?
We were sitting in a meditation position, but after a while it just seemed so formal.

Overall, it was extremely disconcerting! I realized pretty early into the session that if both people are gazing at the other's left eye, there's no "eye contact" - you're watching him watching you. Kind of like life, I guess.
Anybody else have this last experience???
I'm going to work on meditating myself, alone, and getting more used to concentrating on my own breathing, before I try this again.
This was really something.