Do you have an iPhone app on the way? Currently I keep a Mint account for my business which I check frequently on my iPhone. That being said, Mint is just a toy for me; the real work gets done in Quickbooks.
Your pricing seems oddly segmented. Intuitively, I don't know how many transactions I run each month. I'm not even sure how I'd count them. I'm pretty sure it isn't more than 500, but who knows. At the 'enterprise' level (and I'm certainly not enterprise) I would have a tough time justifying a price nearly equivalent to buying a copy of Quickbooks Pro every single month. Especially when my accountant is still going to want a Quickbooks file to prepare my taxes.