SurferTim:
They should work ok together if the devices have different slave select pins. It is a matter of getting them to share the SPI bus.Do you have each device working separately?
edit: I don't know about Xively. Many of these type sites are going to strictly SSL connections, and the ethernet shield library does not support SSL connections.
Yes, separately they work. I can push data up to Xively via the ethernet shield. I can receive data from nRF24L01. But there's something going on when I have both devices connected at the same time.