Funny you should pick this topic, because I just heard this morning on the radio a survey about how much TV most Americans watch each day (on average, its 5 hours)
The radio host asked essentialy the same question you just did:
How do you know when you’ve had too much?
The best answers were:
When you know more on-line people than you do real people
When you tell your real world friends stories about your on-line friends (yet talk about them like they are also real world friends)
When you fall asleep at the screen… and wake up when someone shuts the monitor!
(the other one was about the buttons on the remote, so it does not apply to the CR)