I did try Facebook for Nokia app from OVI store on my Nokia 5800.
Well, if you haven’t been to OVI store yet, open http://www.ovi.com and sign up for an account. OVI store hosts applications for your Nokia phone – both free as well as paid.
Coming back to Facebook for Nokia, if you are a Nokia 5800 user, you might have already seen a facebook widget under your internet and browser section. This is not a standalone application, but a link to the facebook mobile site. What I mentioning here – Facebook for Nokia is a full fledged standalone application through which you can even upload a new snap taken using your phone camera.
Once you sign up at the OVI store, you can download an OVI application onto your mobile phone to browse OVI store, and install application straightaway.
I did download OVI app and installed facebook for nokia on my Nokia 5800 Xpressmusic. The application looks really cool, why dont you try it as well?