Welcome to my new web server. And for the first time ever, it is Linux-based.
I haven't moved because Windows were unstable (haven't had any issues). I haven't moved because of bugs (PHP is buggy on any platform). I haven't got tired of .NET (C# rules!).
I moved because of SSH. I grew tired of plain-text FTP where any kid with Wireshark could get my password.
My hosting company made sure that server change went smoothly. They just switched DNS records and, poof, my website on new server started. It is true that, for a while, there was no CSS or JavaScript but culprit was found in W3 Total Cache plugin. It just didn't like being copied around and quick uninstall sorted that out. :)
There were few other minor issues with upgrade service for VHD Attach and QText but they had more to do with subtle differences between Windows and Linux hosting than with any real error.
Now let's just hope that I don't break everything. :)