I was wondering if I just came up with a brilliant idea, or if...like all other things, someone's already thought of it. To that end, most sites have web hosting packages, however there are some who'd prefer more accurate billing. In this regard say you buy 1Gb Transfer per month, but rarely transfer the limit. My idea, is to have people pay per Mb, and a nominal admin fee per month. Any thoughts ideas etc...? I'm still lacking the boom of business I was expecting with the webhosting services I'm offering, and perhaps this is just the thing to distinguish myself.

I don't think that would work for a couple of reasons.
Web hosting is a service, and as such the customer is usually billed ahead of time for access to the service. What you're proposing is that the customer does not have to pay until after the service has already been used.
I can certainly see people signing up, using the service for a month and then running away without paying for what they used. The way around this would be to check customers credit ratings similar to how cell phone companies do. This way you'd have a better chance of getting paid. But checking credit scores cost money, which will drive the price of your hosting plans up.

I agree with the reply--since web hosts' work is providing the availability of the service, use would be a modest issue for their business model. Plus the additional labor and accounting efforts of tracking the use beyond simple milestones would add a burden that would most likely increase the cost.

The cost of hosting is so astonishingly low today (compared to just 5 years ago) it's hard to see the benfit from the provider's point of view.