My two cents athough it won't count for much - I haven't pick up any on-demand discs but I've heard only bad things about them - people receiving discs that were scratched and unplayable. In general I think a burned DVD has a much shorter shelf-life than a pressed-on DVD, and despite some fascinating titles made available (
Green Slime,
Savage Mesiah,
Carny) I've never been confident enough to pick up any. The prices are expensive too...
Here's a link that might be worth reading (and not as pessimistic as my thoughts above)
Warner Archive DVDs: A hands-on evaluation