Here are some introductory links for the unaware:
Top 20 Educational Locations in Second Life
http://www.simteach.com/wiki/index.php?title=Top_20_Educational_Locations_in_Second_Life
Sloodle
http://slisweb.sjsu.edu/sl/index.php/Sloodle
Second Life & Open Source (client side)
http://secondlife.com/developers/opensource/
OpenACS / DotLRN is due to its community based concept quite well suited as a counter part for SL, which provides in addition to a user-built 3d world with avatars e.g. virtual presence, spacial awareness, instant messaging, multimedia support (playing videos, etc). The interest in SL is especially in the industry very high.
Second Life accepts XML-RPC calls and can be programmed with the Linden Scripting language.
As for the OpenACS/DotLRN conference: Since nobody aside Carlos expressed interest, we have not reserved a SLOT for a SL BOF. Jun, do you have the chance to come to Vienna? Rocael, when will you be arriving?