A humorous post laying out some of the reasons I am switching from Microsoft Hotmal to Google Gmail:
Today I want to ponder the question: what if Microsoft, not Google, had created Gmail? What would be the differences in that web mail client for users today? What if we apply some of the same design rules that brought us Hotmail, for instance?
The new Hotmail Live (or whatever it is called) is crappy.
But, to be fair, Gmail is not all that much better. No one has yet designed a web mail interface I like. Gmail is best of the worst.
Gmail has the best SPAM filter. That’s the main reason I will be switching.
Rick McCharles 
The SPAM filter is great. It uses user feedback to update the filter on the fly. I also like the calender tie in. If your e-mail has a string, “See you Thursday at 9:30” you can have Gmail create an entry in your calendar by clicking a button on the right. It captures the time, location and figures out the date by the word today.