Since my computer was sent away for "repair", I had depended on my iPhone as my primary computing device. It has worked out quite well. The only thing I still find my computer essential for day-to-day tasks is syncing podcasts and watching my TV shows on Hulu. Supposedly, the iPhone Software Update 2.2 will allow for downloading podcasts directly, without the need of a computer. Sweet!
At work, I have been using Mobile Me's services quite often, including organizing things in my personal calendar. It's still too buggy to be dependable, but it sure is slick.