I'm guessing you'll have to rely a lot on your AdWords kung-fu that you talk about so much, because I think customer acquisition is going to be your toughest challenge.
Edit: Actually, I partially take that back. The ads look competitive, but the results look penetrable. Your blog post announcing the site is already #21 for that term, so you appear to be in good shape.
Edit 2: Although you may do well for SEO, I can't help but wonder if you're taking a hit on word of mouth sales with such a generic name that doesn't use a .com. "Have you tried Appointment Reminder Dot Org? My sales increased 10%!" It make work, but I think you're putting all your eggs in the SEO /SEM basket.