I know I, and at least 15 other people will immediately switch if you make Citibusiness Online support work. Check out this thread from Mint's support forum: http://satisfaction.mint.com/mint/topics/citi_business_not_a...?
To make a long story short, Citibank for business is a major bank and there's a lot frustrated people that would love to use Mint for their business, if only they made it work. Meanwhile, Mint has marked this issue as "complete" and doesn't look like they worked on this in 4 months.
I tried using it on your site and it also didn't work.. (stuck on 80% authentication). I realize this feature is in Beta but it looks like you guys already got further than Mint did - their interface doesn't even ask for right information.
I will sign up my business the second you make this work :)