Note that the Libertas hardware is not OLPC-specific; there are random cards floating around
out there, with random bus interfaces. The one OLPC uses speaks USB, but someone else added
support for an SDIO interface. I've not seen one of the SDIO libertas cards, but they must be
out there. :)
Also, while the version that OLPC uses does not use mac80211 due to its unique firmware, there
*is* a thin version of the firmware being developed (alas, still not open) that has a
corresponding linux driver that *does* use the mac80211 stack. It still apparently oopses and
deadlocks as of a few days ago, but it is being actively developed.
Finally, having just finished writing a (non-OLPC) wireless driver using the mac80211 stack, I
must say: kudos to the developers involved. It's a great stack to work with!