I previously wrote about skybook which is a facebook app for Windows Mobile. At that time I was pretty happy with it.
But since then, Skybook has been a big fat failure. More often then not when I attempt to logon I get some nebulous "unable to connect" error. This problem goes completely unmentioned on skybook's website, despite being a pretty common issue.
Good news. Looks like Windows Mobile 6.5 (coming in April) will have an honest-to-goodness Facebook app, and some industrious person has already ripped it from there and released it on the internet. It works on 6.1 for sure, because I'm using it now on my treo 800w. It does pretty much exactly what you would expect, including uploading photos and videos from your phone. You can get it here now.