Yes, I have successfully flashed an LED by 1/2 556. The "on" times and "off"
times are independently adjustable, and all of the values are pretty much
as per usual. With a 4.7 tantalum, I can get the flash rate down to about
1.7 Hz (according to the counter that came with the scope), and, much to
my amazement, with no capacitor AT ALL, it gave a pretty reasonable
approximation of a square wave (admittedly, with a little glitch on the
rising edge) at like over 200 KHz! If I had the motivation, I'd bother
to calculate the capacitance of my ProtoBord, but arithmetic isn't my
favorite thing to do. One thing that I was glad to see happen is that
with the 100K pot in series with the 1K fixed, I actually get a 200:1
range, both for "on" time" and for "off" time, so I guess that means
I can tune the duty cycle from 1% to 99%, and in between them, I can
dick around with the frequency. :-)

Cheers!
Rich