After being tethered by habit for many years to the clunky mail client Outlook, moving my email to the cloud has proved a one way trip. Gmail positives abound:

Most of my older emails from Outlook were successfully imported
All emails sent and received have been retained
tagging of emails is very simple
the search function is very fast
service has been constant, with no noticeable downtime
threads make it extremely easy to see what has been said and done by whom and in what order
I can access and modify all data remotely using an iphone app
Project and contact managers can be integrated into the gmail interface, and leverage my data
Group emails are easy and Google's contact manager integrates seamlessly

There's plenty more, but this gives a good taste. I'll keep looking for something even better, but for the moment the paid version of gmail represents extremely good value for money.