That's a nice application idea. I have some feedback:
* The email subject is labeled "name of your reminder" on the input form and "title" on the confirmation page. I recommend using the term "subject" in both places because that's what people are used to seeing in their email clients.
* I recommend changing "Execution date" on the confirmation page to something less geeky like "Send time".
* The confirmation page should have an edit link.
How will you prevent people from using the application to send spam?
1 & 2 You're right. It was 3am and I wasn't paying much attention to that kind of details :p
3. Yes.
Regarding spam: it's not really useful for spammers because they'd have to send one message at a time. Although they could build bots, Rails 3's security methods offer primary defense against this. Not that it couldn't be circumvented.
I thought about sending a confirmation e-mail, but I deemed that to be an unnecessary layer of complexity - I wanted to build the simplest e-mail reminder service around.
I guess I would edge towards daily IP based limits?
The problem is not so much bulk sending of mail, but sending of unwanted mail from one user to another. Amazon might shut you down if you have a large number of recipients marking these unwanted messages as spam. Perhaps you should record enough information about sender (ip address, unique cookie) so that you can bulk delete and blacklist a problem sender. You can identify problem senders from the unsubscribe link that should be included in the messages.
One of the problems with software that changes how you work is that it changes how you work! There is a lot of resistance to such things--- the user has to see clearly that there is something to be gained with this modification. I like the idea, but I am at a loss to fit it in to how I work...
Well, I suppose on any OS you can find a similar application with Mac's iCal which will send you as many notifications as you want, at the hour you want, without the danger of spam emails.
On Windows there is MonoCalendar and I'm sure on Linux you will find more than one app that will do the same job.
It seems a bit strange to use an Internet application to send you emails ...
* The email subject is labeled "name of your reminder" on the input form and "title" on the confirmation page. I recommend using the term "subject" in both places because that's what people are used to seeing in their email clients.
* I recommend changing "Execution date" on the confirmation page to something less geeky like "Send time".
* The confirmation page should have an edit link.
How will you prevent people from using the application to send spam?