I used to run Outlook at home but after moving to iPhone, I found that managing my POP3 email accounts a pain - I was always cleaning up mail that I've read on the iPhone when I got back ontot the latop.
I tried Windows Live Mail (aka Hotmail) but for reasons only known to Microsoft it doesn't work well with the iPhone and nor does it work well with their Outlook Connector.
So I dumped Outlook and moved over to GMail which can pull mail from my old POP3 accounts at the ISP and also from Windows Live Mail. I can access it anywhere (at home on the laptop, at work, etc) and GMail also works beautifully with the iPhone. So no matter where I am, I can sort out my email once without any need to clean up when I get home.
I love cloud-based services.