Really think there should popup reminders that you can set by date & time & snooze. People don't always see their email when they start their computer.
Agreed completely - either by triggering a Google calendar appointment with date & time assigned (& corresponding reminder), or an independent reminder within Getitdone. Without audible and visible reminders, no GTD App can always pull me away from the chaos of the day at the right time - it may be to late when I get to the "Review" phase. And since moving things that are date-and-time-specific onto the Calendar is a core GTD function, ideally it should be built into this app.
adding another comment:
IF you could make a reminder system in the app, lets say "Remind me 1x, 5x, 10x, etc" and "X before due" with a popup/notification on the screen (possible Snooze button), then you would have a task manager which not only deals with the PLANNING part, but also with the EXECUTION part.