Since you're not going to have a user interacting with the program, I'd say make configuration variable (in an app.config file) responsible for sending/not sending the data. That way users who don't want to report errors can just change a flag in a config file. I'd personally have it turned on by default and then give them guidance on how to turn it off it they wanted to.

You could also have a system tray representation of the service which would show a small notification about any errors and ask the user whether they want it reported or not. I think that it is still better to be able to give the user the choice whenever you are sending 'out' data from their computer.