I'll be completely honest:
As I tell everyone, my entire life is in Google. I use GMail exclusively, and for dozens of email addresses, both personal and business. I do all my scheduling in Google Calendar. There isn't another mobile platform out there that handles GMail better, and after seeing how my wife's [phone that will remain nameless] handles Google Calendar, I have to say I prefer using the calendar on Android which lets me add events to multiple calendars and set multiple reminders.
All that said: the G1 is a piece of crap. I don't mind the form factor, aside from a lack of headphone jack. The problem is the RAM and CPU. It's horribly slow. I've avoided installing about a half dozen widgets, because this thing simply can't handle it.
To somewhat solve this problem, I have one great app that alleviates some of this issue, called Advanced Task Manager. The app its self allows me to see what's running on the system in terms of open apps and processes, and shut down whichever ones I want. A great recent feature was a 1x1 widget I keep on my main home screen that doesn't nothing but stop all unessential open tasks and processes. The full app even lets me make exceptions to this, for example I made my podcast app an exception so that when I have problems running that app, I can hit that widget and everything but that app will close.
This is the best I've been able to do to make the hardware work for me. I absolutely believe that multi-tasking is not the issue here, it's the out-dated hardware that HTC and TMobile came up with to push this really good platform.
I absolutely recommend Android as a platform, but Google is in serious need of some hardware manufacturers to put out some damn phones! And the Hero/MyTouch 3G (what a terrible name) are essentially the same phones as the G1, except the Hero apparently has more RAM, which I've heard doesn't help all that much.
On the other hand, I did try the Pre out recently, and I must say that the keyboard on that thing is not great. Still, WebOS looks slick as hell, a lot more polished than Android, but I'm not sure I like their hardware either.
In summary: the G1 is a sub-par phone, but the Android platform is completely worth it if you're a Google user. If you need to get a lot done in GMail, I think you'll be more productive on this phone than any other.
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Matt