There are two email clients to that come stock, one for gmail, and one for all email (incl gmail if you want). On the 'all mail' app their seems to be a minimum duration of 5 minutes you can set to automatically refresh/sync. No such option at all under the gmail app, just manual. (I haven't checked out any other apps yet via marketplace.)
Now that's pull of course, and what you want is push. Everything I have read suggests that gmail (and exchange too I believe) now does push by default if set up as IMAP. I think that's why there's no sync timer in the gmail app. However I cannot get it to work like a push device. No problems on manual refresh, but just not getting successful push when I test it.
Having scoured the web for help I see many people exclaiming how it works so well, and yet many others for whom it doesn't work at all. I would be interested to see if anyone else in NZ has had success on this hardware or any other Android device. For the moment though I'd recommend waiting till Milestone devices can get the 2.0.1 version and see if that fixes it. I will keep trying though in the meantime and let you know if I find a solution.
I'm not familiar with Google apps sorry, so can't speak to that solution at the moment. Otherwise, this email frustration is the only kink I have come across. I made lots of mistakes on the keyboard initially, but I'm very quickly getting much faster and more accurate. I bet it will be hard to transition from a Blackberry at first though ;). If I recall correctly the Blackberry keys are raised and defined much more than the almost flat Milestone keyboard.
Umm, other thoughts on the device...
GPS can sometimes be a little off, but we're talking around 4 meters or so (sometimes opposite side of the street). It will give you good walk/drive directions based off your location (just like gmaps online as if you typed your location in).
I'm hella impressed with voice search! I'm like a drunk Elvis when it comes to annunciation, but it still does a great job. I need to just say NZ after an address instead of Auckland though because it keeps thinking I mean Oakland. It also can't handle Maori place-names very well, hashing out Whakapapa like a swearword lol. It's super useable though, and better than others I have tried (admittedly many years ago).
Doubletwist is a great blessing for adding media from your PC, because it re-formats videos for you on the fly. I was manually re-encoding via VLC until I downloaded that software to my PC and it is so much easier. For other data though (eg zip files) you can simply treat it as removable media in Windows. Media player is great (wide range of alternatives in marketplace though). Screen is crystal. Speaker is nice and loud.
Form factor is sweet. Slides into pockets easily and doesn't feel fragile. I though it might be too bulky or square but it's not at all. I think being so thin helps a lot.
Camera and video working without issue. I'm sure I must be due to be hit by the 2.0 bug soon (discoloured photos), but seem to be free of it at the moment.
Hope that helps. I'm sure you'll enjoy it if you purchase one. I just can't give a very clear answer on the email vs Blackberry sorry.