For me, the iPhone works and works well, but it can be improved upon. Turning on and off the wifi is a multi-step process. Adjusting the brightness too, is a pain in the butt. However with SBSettings, it is quick and easy from within any program.
Moreover, I want to see my calendar information easily and everytime I turn on the phone. LockCalendar helps me to keep track of appointments.
I also forgot about my latest Cydia install and purchase, BiteSMS. It allows me to compose or reply to any text message without closing what I'm doing. So if I'm in Safari and my wife sends me a text to get up off the couch and come to dinner, I can reply to tell her to leave me alone while I continue to write this post to you. (I'm joking about the dinner story, but you get my point) BiteSMS is what Text Messaging should have been on the iPhone OS.
I don't get into skinning and changing all the backgrounds and icons with Winterboard, skinning the iPhone 3g slows it down too much for me. If I had a 3GS I would probably run Winterboard to change the look of my phone for fun.