During July - September 2009, I spent about one month total in Mexico. Two separate trips, one to Oaxaca in southern Mexico, and the other to Tula, Hildalgo which is near the capital. On the second trip I had an opportunity to spend some time in the capital city.
I carried a medium format camera with me, which garnered very few looks. I was somewhat surprised by that. I suppose they are used to crazy gringos.