First of all, I'm using my iPhone to post this entry while lying on the bed, and playing with my kids (tickle-tickle as Princess called this game) so please excuse any typo error - this particular reason is more than enough for me to love this piece of gadget.
Other bonuses are: I use my iPhone to read and quick reply to my emails - too easy to do that from our kitchen up to our parking area specially after I changed our Wireless AP to Apple Airport Extreme N-Draft - the range and speed of my wireless is really amazing.
To catch up with my favorite websites after a busy day I usually subscribe to RSS and read them thru Google Reader easily which is perfectly optimized to iPhone.
Driving going to my work for almost 2 hours a day; iPod part of my iPhone is always my companion while listening to tech podcasts and audio books - no wasted time while stuck even in traffic.
Schedules, reminders and alarms are also very important to keep my life sync.
Oh yes, the 2Mb camera of my iPhone never let me down whenever I want to capture a moment.
Similarly, the built in Notepad and Erica's Voice Notes are always there every time crazy idea pops-up in my head - to capture it and later see where it fit in my getting complicated life puzzle.
I can reboot our servers, back it up, execute commands - do all controls thru SSH, anytime, anywhere.