What exactly does more capacity get me? Trilogies on one disc? More special features? Higher.... errmm, def?
[ Thus I begin my research in preparation for the big holiday buy ]
well, that's a good question.
It of course, for a pc/mac/*nix data storage issue (if high capacity optical does catch on in that application... which is another debate of it's own...) certainly more on one disc is nicer than less.
For entertainment, it could make the movie high-deffier, particularly if they are long-running times, thus allowing the maximum instantaneous data bitrate (which BD does still hold an advantage on... but for a very lame reason* see below!) to be sustained for more of the film. Or it could be for inclusion of additional extras (IME features, multiple language audio tracks, etc) . It could also allow things like TV shows to be sold on less total discs (say 6 episodes per disc instead of 4)...
The main point of my post was simply to knock the BD FUD department who trumps out their 'list' of BD advantages, #2 or #3 on the list is 2L 50 GB discs vs. 2L 30/34 GB discs . This despite the fact that only about 50% of BD releases to date are on BD50's (because the manufacturing yield is atrocious and there are only 3-4 working lines worldwide) while about 80% of HD-DVD releases are on 2L HD30's.
*the bandwidth theoretically is useful because of course, in theory, more data = more definition. however* many BD titles until this summer were encoded with MPEG-2 (because sony owns it!) which requires a much higher bitrate to achieve the same minimal 'lossiness' as more advanced MPEG-4 and VC-1 codecs running at approximately 50% the bitrate. newer BD titles using these advanced codecs have seen far less of the available bandwidth used! hahaha! the bandwidth is also theoretically useful for BD as it champions uncompressed PCM audio tracks , which of course, are nice but practically useless to 99% of the HT market who can't afford amps/speakers that offer less than .1% distortion. nonetheless, it's an interesting talking/marketing point- lossless audio combined with HD video. (hd-dvd offers dolby truHD {another lossless format} and dolby digital + 1.5 mpbs typically... )