Setting up email is really easy, i use google apps and also several gmail account, simply put your address and password in and it sets everything up.
Bottom line is blackberrys keep you in touch with the online world and you will receive instant messages, no fuss and sync perfectly with google calendar and contacts. Plus you get all the nice to have apps like facebook / twitter / barcode scanning / maps / etc etc....
It isn't particularly fancy but its the function of push email and solid operation that appeals to mainly the business crowd and geek/gadget lovers.
Take a look at
BlackBerry Forums at CrackBerry.com
If you do get a blackberry i really recommend OS 5.0, its a big step up but only available in beta form. You can find info on crackberry.
Having said this, i'm religiously following twitter and google public waves daily about the nexus one, i really hope it comes to the UK in Jan. I'll have one, i think it will turn out to be one of the best phones ever released. As the G1 is available on anroid market to developers for $300, rooted and unlocked, i'm hoping the N1 will be similar, which would be great!
Regardless, the 3 phones you have mentioned are all great in their own way and you won't be disappointed with any of them. All of them are the new gen of phones capable of doing pretty much anything on the move. Just remember if you get a carrier locked android, it's unlikely you will be able to upgrade the OS unless the carrier releases it or you can somehow root your phone.