I'm missing my E71. I didn't really had a chance to properly say goodbye. Weird, I know, but it was my trusty sidekick for almost 2 years.
The X10 Mini Pro isn't a direct replacement. The applications are the main "actors", and not the basic phone functions like calling & sms-ing.
I chose Android because of the availability of apps that extend the desktop to the mobile realm. Tools like Remember the Milk, Evernote, Dropbox, Wordpress, etc.
The other reason is because of the open nature of the Android OS, which is why I didn't get an Apple iPhone. The iPhone is too ubiquitous anyway.