Firstly, to the previous reviewer who had issues with it displaying at the incorrect time, you might want to check your clock settings, as I never had an issue with this program displaying the alerts incorrectly while I was using the demo nor when I purchased it. Perhaps something wasn't set properly in your clock settings and is causing it to conflict with the program? ( Just taking a wild guess )
Anyway, onto the actual review. This program is absolutely fantastic and worth every penny of purchase if you forget things a lot or want to get yourself on a daily / weekly scheduled routine. I struggle with aspergers, and it's very important for me to be on a regular schedule with medication and activities, but I'm extremely forgetful. I tried 10 other reminder applications for macintosh, and NONE of them worked as described. They either relied on another application to function (ex: ical, palm, etc) others would just crash upon startup, and some were just too dang confusing to figure out how to setup a reminder.
I'm On Time, has a very simple setup that takes all of 5 minutes to learn how to use. It reminds you at exactly the time when you set it too as well. The growl feature is nice as well, however a small tip - if you have growl turned off, you will need to turn it back on, quit I'm on time then re-open it so that growl can function with it. ( I didn't know this ). Other then that, it is a wonderful program, and I'm looking forward to future versions of it!