CalDAV is the Open Standards approach to calendar sharing. It is a little bit late to the game, but adoption is accelerating. Support has been announced by vendors such as Apple and Oracle. The Open Source community has a number of projects underway to utilize this new standard.

General Articles on open calendar sharing:
http://software.newsforge.com/software/06/02/09/2140226.shtml?tid=74
http://ietf.webdav.org/caldav/home.html
http://www.educause.edu/LIVE057
http://www.sscnet.ucla.edu/blogs/consortium/archives/000445.htm
http://tinyurl.com/ya8b8z

Open Source Projects:
Cosmo (CalDAV server) - http://cosmo.osafoundation.org/
Chandler (PIM / CalDAV client) - http://chandler.osafoundation.org/
Mozilla calendar clients - http://wiki.mozilla.org/Calendar:Home_Page

I gave a presentation at the 2006 Florida Association of Museums Conference (FAM) in July. I gave the same talk at Denison University in October.

Summary:
Avoid vendor lock-in. Preserve your ability to access your own data into perpetuity. Adopt open standards.

The slides are posted on the web:

UPDATE 10.17.2012 - The original links fell victim to Internet Information Decay. I mirrored a copy of the presentation here:

Introduction to Open Standards and Open Source Software (PDF)


These original links to the presentation are (sadly) no longer active:

http://www.flmnh.ufl.edu/omt/presenta...ndards.odp (Open Document)
http://www.flmnh.ufl.edu/omt/presenta...ndards.ppt (Microsoft PowerPoint)
http://www.flmnh.ufl.edu/omt/presenta...ndards.pdf (PDF)

According to the Go Open Source web site, Go_Open was the first television series dedicated to Open Source Software. The television series aired in South Africa as part of a campaign to promote open source. Here is a fast mirror to those videos:

http://www.flmnh.ufl.edu/linux/go_open_source.htm

UPDATE 05.01.2013 - The original fast mirror I posted has been taken down. The go_open videos are apparently still available in the Internet Archive at:

http://archive.org/details/go_open_season_1

Just wanted to say hi to the local Linux Users Group here in Gainesville, Florida.

http://www.gatorlug.org/

Here is their cool logo: