It seems pretty easy to define myself by my work. After all, it's interesting, prestigious stuff, and I spend a larger proportion of my waking time on it than on any other single activity. I sometimes have to refocus on essentials and recognize the job for what it is: ephemeral. I came into it, and eventually I will leave it, and I will still be myself. I think a lot of people lose sight of that, and come middle-age, or retirement, the fact that a job isn't forever hits them like a ton of bricks. I'd rather spread it out, myself.
As for what I'm doing... I can only write in general terms at this point. I'm pretty solidly on the project management side now. We're getting closer to shipping the first units (we have two in Taiwan for evaluation), and so most of my work is controlling and directing flows of both experimental work and production work in parallel. It's pretty high-intensity, and I think I haven't gone more than half an hour without interruptions in the past week. Fortunately, I deal pretty well with that, at least when I'm not trying to do Serious Work of my own at the time.
Another tough thing to deal with is that old perfectionist streak. I'm not the only one who has it, I know. It tends to drive me to work harder and stress out more than I should, and so I have to keep it from going nonlinear and taking over.
If I seem a bit sharp-edged these days, it's because I'm still working on tuning that separation. Naturally, my employers will take all they can get of my headspace, but I need to keep my core focussed on things which are ultimately more important.