At this level a build in flash is actually considered a hindrance. Minolta were heavily criticised for putting one on the the old 9. Personally I thought it was good.
It would have been nice but if i had to choose I would take that viewfinder over a flash any day.
There's been a lot of bitter fights about this the Canon forums (as if there isn't always...) about the teasers that show what is assumed to be the 5D successor, with a line on the viewfinder which seems to suggest a pop-up flash. People are pretty cut up about it.
My take, what Nikon did with the D700 was good. If they had made the hump a millimeter or two wider, they could have given it 100% coverage too, I don't think anyone would have complained about the additional size.
Hehe, that happens to me with the 24-105L too but only if I have the hood on - I guess the flash on the rebels sits somewhat lower. But in all fairness, barring the lens getting in the way, the pop-up flash is not bad. I wouldn't take the dedicated flash gun with me for travelling, because I know the only time I would need/use a flash is for fill or "pub pictures" fairly close up, and I'd be using the 35mm f/2