Not to sound like too much of a homer, but in my opinion, LwMesh is great.
I designed a board around the ATMEGA128RFA1, using the data sheet as a reference. I downloaded LwMesh, made a few tweaks to IDs in the Peer2Peer project (i.e., APP_ADDR and appDataReq.dstAddr), and flashed it to my board. And it worked. The first time. There is something particularly satisfying in observing wireless transmission for the first time in a personal project.
The demo applications included in the LwMesh package make it easy to get up and running with the stack with my own application specific software.
I'm sure I'll be here, hat in hand, asking for help with a stack problem at some point in the not to distant future. However, at this point, everything seems to be working great.
To anyone else in the AVR world new to wireless applications and trying to get their feet wet, I recommend using the LwMesh stack.
Alexru: thanks a lot for steering me towards the ATMEGA128RFA1 when I was here asking about the TI CC2530 a few months ago...