1)-getharvest.com -mint.com -box.net -dropbox.com -basecamphq.com -xero.com
As you may have noticed, these are all web application using one major color to make things a little more appealing. They all use pixel perfect attention to detail. From a first impression perspective, a solid design really counts for most users.
2)Google Calendar integration, Google Apps addon, Custom branding(which is on your todo list), online payment processing.
3)I meant exporting the appointments into a Google Calendar. Like you have mentioned, you can use the API to add the appointments into the calendar. Maybe even add an alert.
4)Custom fields would be a great idea. Very useful.
5)I agree, but there's no harm in having a look. Try www.domai.nr. It will abbreviate or remove vowels to make your url shorter. It will also show you different TLD domains you could use.
6)Great idea. If you want, you can add a small light colored link below the main box that links back to reservv.com.
7)Even better. That way you won't have to deal with any refunds. Good idea.
If you have any more questions or you would like my opinion, let me know. Good luck with your application!
Karl