Last time I looked they have a minimum bar of $250,000 of business a month, or they're not interested in you. Thus not an option for people starting out.
And, dare I ask without sounding like a complete user, what would you use if you were only doing < $1000/month. Would a credit card processor even touch you or is it basically just paypal?
Paypal and Google Checkout are both good alternative options to look at. In some cases when you factor in all of the upstream credit card processing charges you'll even pay less.
This discussion is probably dead, but just in case:
Within the last year, I've been in the position of doing <$1k/month on a credit card processor, and it was actually a delightful experience. The company I originally worked with was bought/renamed or something and I haven't had to deal with them in quite a few months, but I can probably dig up a contact. Email me if you like.
They don't have any exceptions. I paid for the rails SAAS kit and then talked to Braintree and it took a week's worth of email just to get them to send me the application. They told us that if we didn't do enough volume they would cancel our account.
I ended up just going with Payflow Pro (Paypal). Had to rewrite most of the SAAS kit..