I've seen slight differences that make the 51FD better than the BD30. I definitely don't think it's a HUGE, HUGE difference, but it is better, PQ-wise.
Colors look better on it. I don't think that it necessarily has to do with the pairing of the 51FD with my Pro-151FD television, either. I think pairing it with any quality television will yield some appreciable differences.
It's currently slower than the BD-30 at initial load times, but I can say that the responsiveness when navigating the menus is certainly much smoother. That's even with the majority of the discs that I play on the "Demo" firmware...
While it's 'currently' slower, I can only imagine they will improve the load times as the player gets new firmwares.
"Outside of a dog, a book is man's best friend. Inside of a dog it's too dark to read." - Groucho Marx