I'm an addiction doc, I mean I work with people with problems due to heroin, to cocaine, to alcohol and the so... and, well, yes I am addicted to my n800 :-0 (it's a joke, I am not *clinically* addicted) as well as I have been to a number of info gadgets, the first of whom was a texas instruments ti 57 programmable calculator.
How you know you are addicted to something? There are some official criteria which are quite generally used in clinical as well as legal environments, but, as a rule of thumb, when your interests and pleasures do get restricted to only one behaviour, or substance, which is repeated and repeated even in face of perceived negative consequences, and you possibly experience tolerance - in the sense you have to increase your dose of that behaviour to experience a good feeling - and dependence - without that behaviour or substance you feel bad -well you are addicted, and possibly you might need a professional help.
Now think of your use of the n800 or other gadgets and make your diagnosis by yourself...