For me, the big thing was also the Calendar sync'ing. For a while now, I've been keeping my Google Calendar sync'd with Thunderbird at the office. With my old phone, I'd have to enter important reminders for myself separately because the phone's scheduler didn't sync with anything. Now with a smartphone, I can keep everything sync'd up no matter where I am and it's great. It really was one of my main reasons for getting an Android phone.
Plus, if you're a sysadmin for any Linux systems, check out the ConnectBot app. Full ssh session from your phone!
