I upgraded on 4/22/2013. It asked whether this was an upgrade or a custom which would have been a clean install (I suppose). As far as Vista is concrned, I never experienced any issues with it until early April when I could not perform backups. I did have a copy of my documents and pictures folder on my external but because the upgrade to W7 took place so smoothly, and I was able to do a system image and daily incremental backups, I no longer needed those two files so I deleted them from the external.
I did not do a clean install because I could not even begin to tell you what was on the hard drive.
But, what's done is done.