Interesting idea. This would definitely ease the burden on consumers once you got many of the major companies that everyone pays bills to onboard. The only problem I think you might have is something similar to what Mint.com and other similar sites have had to overcome, which is getting companies and consumers to trust you with their sensitive information. You would have to offer a distinct value to the companies to get them onboard, otherwise why would they use your site instead of what they've already spent money on to get their own site up and running? If you can clarify that value proposition for them, I think it's a viable idea.