Has anyone had experience with hosting sites that offer pay-per-MB rates? For instance, www.nearlyfreespeech.net offers 1-cent per MB per month storage space and $1 per GB bandwidth. This seems like a really good deal to me. I don't need too much storage space, but I'm not really sure how much bandwidth I require, so this ensures that I only pay for what I use. Or is it better off to go with a flat-rate (yearly) plan?

It depends on how much bandwidth you use as to if its a good deal, im currenly using up around 50% of my alloance of bandwidth per month, and the price is a fixed rate and it seems quite reasonable. I think the best thing you cna do is get a moderatly cheep host and see what your bandwidth is sitting at. Then once you know this you can work out the best deal.