If you keep getting errors when trying to set a custom page tab icon when adding an app to a page – make sure that the application is actually published. You can add it – and the icon will change, but will still generate an error – if the application isn’t published yet. No idea why it’d give an error like that, but hey.
There’s quite a few other reasons for the error as well, but Google have probably already told you about those.
I spent the evening making sure the different pages on Gamer.no gave relevant titles and descriptions when shared on Facebook. The implementation was quite straight forward, but finding the finding the actual documentation for which elements Facebook supports ate a bit of development time. After navigating through four or five wiki pages at the development wiki describing various parts of the Facebook Share system, I finally found the page getting down to the metal about which elements you should include.
The page can be found at Facebook Share – Specifying Meta Tags.
We’ve currently implemented title, description and medium. We also had image_src, but decided against it at the moment – the first feedback we reserved made it clear people preferred to select their own image. This may however be because of the first batch of people being a bit too technical competent, so we’ll probably use image_src later (.. does Facebook support providing several images through image_src?).