It has to be big
Finger's crossed I've yet to find a bad BD. (Although I only have about 20 so far.) My in-laws have 40" HD televisions and, at normal viewing distances, I really don't see much difference between DVD and BD.
I have a JVC HD video projector and an 84" screen. Watching it from 3 metres away is really like being in the cinema. I have both BDs and DVDs of several titles, Zulu, Italian Job, Sin City, Time Bandits, Big Blue, 2001, Where Eagles Dare, Ipcress File and so on. Without exception the BD is superior to the upscaled DVD; and the upscaling on my Philips player is extremely good. (The remastered Basil Rathbone Sherlock Holmes DVDs look very good when upscaled.)
And, as someone said earlier, Blade Runner on BD has to be seen to be believed.
Some people have criticised BDs for showing grain - sorry, but that's what I want to see - if it's in the film I want to see it on the screen. If the studios start to filter out the grain then we'll lose resolution.
To whomever mentioned that you won't see high def Charlie Chaplin films... why ever not? They were filmed on 35mm nitrate stock, that's generally pretty fine grained and each frame is more than capable of holding more image information than can fit on a BD frame. 16mm film is a different story. I have a large collection of 16mm prints and some are about the same standard as BD but most prints are far inferior.