I did in May, but I didn't have 100% success rates. I set the duck eggs 7 days before the chicken eggs went in. I had 15 out of 19 eggs hatch (well I had tossed out 2 duck eggs early on I think due to them being clear) and I had less success with the chicken eggs, but I did have 3 of my own chickens' eggs hatch and 3 of the realsilkielovers' eggs hatch. I lost lost of silkies and showgirls I'm sure, as that was my first incubating/hatching experience and I tried to help some of them hatch, but ended up doing them no real favors. But I did have ducklings and chicks hatch out in the same incubator within about 5 days of each other. I think I drowned some of the chicks by upping the humidity for the ducklings to be ok, and then when I opened the bator to take the ducklings out, that didn't help the chicken eggs either.
I probably wouldn't do it again if I didn't have to. I think keeping them separate works better. I did it with Guinea eggs too another time mixed with chicken eggs. Same sort of problems...
Good Luck
Lisa