You have to reconfigure your VST paths. Cubase 7.5 is a separate install from previous versions, so you’ll also have to reconfigure your preferences. Thankfully, you can have both versions opened side by side. This makes it easy to copy your preferences and plugin paths, which I prefer doing than copying preference files (just seems a safer way to me).
I also had to re-register (not really, actually) my iLok EWQL Spaces plugin, but it was super quick. You may see a pop up window come up as you load a project if you happen to have this particular plugin. This may also be the case with a few others iLok plugins, but it only took a few clicks to get it going again. No big deal.
So far, all I can say is that C7.5 is THE BEST Cubase I have used thus far. The new features are awesome and the new look a noticeable improvement from previous versions. Cubase looks more professional now, IMO. Still too early to call it, but I’m really liking what I see. It’s been very stable with heavy projects as well. No complaints yet.