Just built a quick project with the DHT11.
The doc here - https://github.com/electricimp/reference/tree/master/hardware/DHT11 says to use a 1K resister.
But the source code here - https://github.com/electricimp/reference/blob/master/hardware/DHT11/dht11.device.nut says to use a 10K one.
I tried both, no huge difference.
Interestingly, though, the weather service reports 71% humidity. Here in my study with the window open the DHT project says 38% and the Imp sensor tail says 55%. Tried two DHTs, they were essentially the same. So who knows?