This looks like a great plugin to use! There is a website that is in great need of a redesign for a potential client of mine: http://www.rustgod.ca/. His current booking system is giving him a lot of trouble.
Appointments looks like it will do everything that the website needs except I am not sure if it can handle current deals/promotions going on. Is it able to? Also, does it work well with dealfind, groupon, etc.? For example, only people with the groupon coupon will have 50% off of services.