@seolondon:That would depend upon how you perform the update. The Store route seems to be 100% conversion. I.E., things are left in 8.1 with 100% of apps converted. If you do the "in place upgrade" (not via the store), it seems to uninstall everything.
You are left with a "windows.old" folder holding everything it cannot upgrade.
The only thing I have found that it seems to not like is .NET 1.1 apps. While this is logical I have some 1.1 apps which cannot be upgraded. I was able to re-install the 1.1 framework despite the OS and things "work".