I use Paytrust, but since Intuit bought it, they've let it go downhill. The problem from a business standpoint is that it's hard to compete against free.
It's also pretty hard right now to crack the market without a lot of capital, because there isn't standardized electronic bill presentment that works in a high enough percentage of cases. Therefore, you have to web-scrape. Paytrust bootstrapped this by having billers mail paper bills to them, which they would scan and manually enter the amount due. Since virtually everyone receives bills online now, the paper API isn't really viable.
If someone came up with a common format for bills which included some metadata like amount due, due date, name of biller, plus HTML or PDF for the actual bill, it would be very useful. Then there is the question of delivery. Most banks don't want to deliver the full bill by email -- they want you to log into their site. If there were a standardized API with the ability to authorize third parties, it would make things much easier.
The only real opportunity I see is for Intuit to bring Paytrust into Mint. There could be a lot of integration between the two, and the attention to detail that Mint has could make a world of difference to Paytrust. Right now (insanely) you can't even export your paytrust transactions to Quicken, because a number of years ago, Quicken stopped supporting the QIF format, and this is the only format that Paytrust exports.