I have finally gotten my iPhone, Google Calendar and iCal working seamlessly.
I like to keep my Calendars on-line, so Google calendar is great. I have Spanning Sync which syncs both ways with my iCal. When I make a change on my Phone, I can sync with my Mac, which in turn syncs with Google Calendar.
All of my email runs through gMail first (amazing & teachable junk filters!) before having them forwarded to an IMAP account that keeps all of my computers (yes, I occasionally use a PC) on the same page. I also use gMail for archiving all of my email (I even BCC it and have a rule for my mail to go into the "sent" category). But I still like to read it for the most part through my mail client(s).