One of the things I noticed on the HD2 as soon as I unpacked it, is the seemingly old version of Facebook that came installed. Mind you, I am running the latest version of the ROM from http://www.htc.com/nl/supportdownloadlist.aspx?p_id=297&act=sd&cat=2. The actual download-page for the ROM upgrade will also tell you how to confirm which version you are running of the ROM (which is easy to check via Start > Settings > System Information (or Software) and then version.) Note that the download-link is for the Dutch HD2 ROM. Please use the HTC Support site of your country to find the appropriate one for yours.
The version of Facebook Mobile that was installed was version 1.0.0.7 (from the top of my head) You can verify your version by going into Facebook, then at the home-page click Menu followed by About.
Now to upgrade to a higher version, you can use Microsoft Marketplace (which should already be installed on your phone) Simply search for Facebook and it should find it. Install it as normal of course (as a tip; be sure to set Microsoft Marketplace to store it’s files on your SD-card)
If however it doesn’t, click on Menu followed by Settings. Change the region to United States – English and click on Save. Now try the search again and it should find it just fine.
I have of course made sure that the HTC Sense UI still maintained the Facebook functionality amongst my contacts – which I find incredibly handy. It of course did – and I have since rebooted the phone (You might be asked to reboot your device as well)
So now I am running with a far more usable version of Facebook mobile on my HD2. Oddly enough the app still is in Dutch, but you can’t have your cake and eat it :-)