Today I went to an interesting guest lecture given by Wei Hong, Co-founder and VP of Engineering at Arch Rock Corp. - a Berkley spinoff. He was talking about the tiered, IP-centric architecture of the low power wireless network platform designed to seamlessly integrate with the internet or intranet through the native TCP/UDP/IP protocols and Web Services.
Arch Rock are working on 6LoWPAN - a low power usage version of IPv6 for WSNs (wireless sensor networks) based on IEEE 802.15.4. The routers do the 4-6 translation. Really cool stuff!
The SunSPOT SDK v.2.0 currently has a LowPan implementation build on the 6lowpan draft, including support for mesh routing using an AODV derived routing manager and all of the hooks are exposed to implement IPv6 on top of this - but no working IP layer so far. 
Could be so nice, to be able to ping those nodes. I am unsure of the status in the upcoming v.3.0 SDK.
But the guys over at Sun Labs are still having fun. They are currently working on an after-hours project strapping a SunSPOT to a high altitude Balloon - sending it to near space 