What do you want to book from a directory ??
I can let bed and breakfast/pension houses do the booking through my site though I am still contemplating on that.
Anyway, yes it is a good feature for classipress for a specific purpose and if there are a lot of users clamoring for this it will likely be considered.
I think the development theme is currently working on improving the basic and general features of Classipress as a classifieds site platform but I will try to refer this thread to them so that your request will be evaluated for consideration.