After 900 accepted shares, my U seems to be a little higher, but I'm going to leave it for a while.
BTW, why does cgminer occasionally (after about 50K shares) stop sending work to the BFL box? It stays running and shows longpolls as they come in, but no shares...
I'm observing something similar, but not your quoted 50k, in fact it seems pretty random here, I will need to do more logging; had logging off so I wouldn't clutter the Raspberry SD card.