If someone wants to track your phone and are capable of doing so, then they obviously can do it regardless of whether or not you have a Nokia account.

I dont think there's sufficient information collected in creating the account itself to perform espionage... if that's necessary, all the information, including the ones that you provide during account creation, can be gathered by monitoring the activity that goes on in your phone directly, yes?

Just tracking the GPS data alone will suffice to point exactly where you live (your phone communicates with the Nokia maps server for this). Your browsing data/call records/msgs can be monitored... but then again, that will only happen if someone is incredibly interested in what you're upto. Otherwise, I believe Nokia have other more pressing issues to deal with at the moment.