I would say GMail is a pretty big success...

Yeah, it's missing a lot of "features" but it's terribly simple and useful and takes care of the spam issue for me with less effort on my part than any other solution I've found.

Also love the more or less instant searching of all my email. I used to fastidiously sort all my email into folders and create rules to do so automatically because it took outlook so long to search my email. Now it's simple and natural. I just never delete anything and when I want something old, I search for it and find it almost instantly.