From about 2000-2005 I spent a lot of time taking photos at night, inspired by a class I took with Lance Keimig, and later by expeditions with various other Nocturnes including Tim Baskerville and by looking at the mind-blowingly amazing work of their colleague Troy Paiva.
Below, one of the photos I'm more fond of, a roughly 20-minute exposure taken near Kendall Square in Cambridge, MA at about 1AM:
I've drifted away from photography in recent years, though, and with changes in work and life it's also harder to regularly go out shooting until 4AM.
Jotting down a few links to other photos-- I'll post more and organize them some day... [2011 edit: it's been 6 years and I still haven't organized them or scanned most of the negatives. Oh well.]