I've just built a few nodes using the EasyPCB Rev 9 RFM69 Edition and I can confirm it lives up to its name - build takes only 15-20 mins, and node works first time because there is no chance of incorrectly wiring the radio. Thanks @sundberg84!

The PCB fits nicely along with 1 or 2 AA batteries into the 100x60x25 project boxes available on eBay for about $1 each:

Easy PCB in 100x60x25 project box

(AA battery holder is actually about 1.5mm too long to fit - I've cut off the non-spring end of the holder, and the positive wire is held by tension between the +ve battery terminal and the side of the case. Ugly, but fine for nodes that don't get moved around. White tape is to prevent antenna from shorting against the top of the radio module.)

I have a couple of observations that might be worth considering to make the next revision even better:

According to the MySX specification, MySX header pin 10 should be connected to Arduino pin D4, not D2 (which is already used for the radio)?
It would be handy to have a bit more space between the voltage booster and the adjacent cap - boosters with pre-soldered right-angle headers don't fit without hiting the adjacent cap (see photo). You could free up some space for this by mounting the battery measurement resistors vertically. (There is a risk that this might cause the voltage divider circuit to pick up noise from the adjacent booster; which might cause a bit of random fluctuation in the battery voltage readings. I suppose you'd need to do some tests to see if this is actually an issue.)

photo showing booster hitting adjacent cap

I put a few layers of insulating tape under the RFM69 so that it sits about 0.5mm clear of the PCB, to make it easier to desolder if the need ever arises (see photo). It would be nice if there were holes in the RFM69 pads so that it could optionally be mounted via 2mm male/female headers. You'd need to make a small adjustment to the antenna length if actually using headers, but otherwise I don't think this would affect the radio's performance.

photo showing tape under radio module

EDIT: You can surface-solder 2mm headers to the existing pads, but it ain't pretty:

RFM69 mounted on 2mm headers

You can mount a DS18B20 in the prototyping area!! (requires wire soldered under PCB to arduino input pin)

photo of DS18B20 mounted in prototyping area

I think the 4k7 pullup resistor for DHTxx/DS18B20 temperature sensors should be on any pin other than D3. The only (easy-to-use) hardware interrupts on the ATMega328P are D2 and D3, and D2 is already used for the radio, so D3 should be reserved for sensors that require an interrupt (e.g. motion sensors, buttons, switches).
In fact, the space taken up by the pullup resistor might be better used as a second prototyping area. If you bring out some arduino IO pins to this area, you could actually connect a pullup resistor to any of those IO pins. It would also be good to bring out some of the IO pins that aren't already brought out on the MySX header. Suggested layout (apologies for literally-back-of-an-envelope sketch):

sketch of suggested prototyping area layout

Hope that's all useful / constructive.

Thanks again for designing this awesome PCB!