Found via "PreCentral.net - http://www.precentral.net/app-gallery/app-catalog/facebook", the Facebook client for webOS has been upgraded to 1.3. I just loaded it up on my Palm Pre and it looks great. New features include:

1. Landscape mode.
2. Photo tagging.
3. Filtered news feeds.
4. Performance improvements.

The developer's page is here with more details: "Facebook for Palm webOS - http://www.facebook.com/apps/application.php?id=4620273157"

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Updated 2021 : note that the above post was originally published in 2010, but is left here for archival purposes. Sadly, webOS for mobiles is no more, along with the original Palm company, so all of the above links are now dead, and have been unlinked.