I would love to hear some discussions on this. For example, I wonder how much it matters how tech-savvy users are? I'm currently looking at a mixed model at
http://pagekite.net/, pay-as-you-go for bandwidth usage OR tiered monthly subscriptions for heavier users and businesses.
I had kind of assumed that the average joe would prefer pay-as-you-go and companies would go for a subscription - your comment suggests I may have it backwards... :-P