The calendar was my biggest gripe on the Pre as well. I've only had a couple of hours to use it, but there are several big differences:
1. The Calendar widget can be added to one of the 7 screens in a scene. (This may not make sense unless you watch a few Hero review videos.) This means that the calendar can be very accessible, only a swipe away from the Home screen. With webOS, you have to launch the Calendar and leave it open as a card. My personal preference with webOS is to close apps when I don't need them, so accessing the Hero's calendar wdiget is faster and more convenient for me. Some webOS users don't mind having multiple cards open.
2. There is much, much less lag time in the Hero calendar when switching between days. The response is nearly instantaneous. Clear advantage to the Hero here.
3. The Hero calendar still uses those damned scroll wheels to select the From and To dates, but at least the scroll wheels show the day of the week -- the Pre scroll wheels do not. Also, the Hero scroll wheels are bigger and less "sensitive". It's easier to select the date you want without scrolling past it.
4. The Hero calendar has an Agenda view. There is also an option to view only the appointments in the daily view, or view the entire hour grid for the day. I prefer seeing just the appointments, but unfortunately you can't swipe sideways to change the day you're looking at. Unless I'm mistaken, you have to push the back button to get back to the month view and then pick another day to view. The Pre's compressed time view is very nice -- the Hero doesn't seem to have a comparable option.
5. I am amazed at the number of settings and options offered by Android. You have to patch webOS to add the simplest options, like defaulting the calendar to month view. There's no need to patch Android to add the settings that Palm inexplicably forgot -- they're already there. In this respect at least, Android is definitely a more complete OS than webOS.
I hope that helps. So far, I like the Android calendar better than the Pre's. It syncs with Exchange and other calendars, like Google's, and events from different calendars are displayed. You won't be giving up the Pre's combined calendar views if you switch.
If you think of any specific questions, let me know.
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