Check if your oggs appear under '(unknown artist)' at the bottom. All my oggs show up there because for some unknown reason Media Player isn't picking up the tags.

I was quite frustrated with ogg playback in the NITs since I upgraded to Diablo. Luckily Canola beta 10 just came out (it's still not officially released, but it's available in the extras-devel repository) and it works as a charm.

Cheers.