Two good sits yesterday: 25 minutes before work, 30 minutes before bed.
I found it particularly useful to concentrate on the "third eye," between my eyebrows and at the top of the bridge of my nose. Not necessarily focusing on the pressure that tends to build there when I concentrate, but just being aware of that particular spot.
The reason I did this initially had less to do with the chakra and more to do with the concept of "nadis." The third eye is supposed to be the spot where the nadis converge, so it made some sense to me to focus on my breath where it converged at that spot.
Concentration was very strong doing this, very calming, very peaceful. I think I may stick with this technique for a while.
Another technique I've been doing a lot lately has been something like centering prayer (ala Alan Chapman's method on page 52 of this ebook:
Three Steps to Heaven )
Not much to say beyond that right now.