1st of all it's very nice application. Thank you very much!
I'm not sure if that is bug or just simply there is no such option, but Songler doesn't scrobble any of my mp3s played with Media Center.
When you read history of added features you can see:
1.3.0. Added the ability to Scrobble music you play in Media Center to last.fm too.
It sounds like Songler should scrobble not only last.fm music but every mp3 as well.
If everything is working as intended such an option would be very welcome. What do you think?