Where I work there is a blocker and believe me it works very well.
When you try to access a blocked site it tells you that the company has blocked it. This however is not blocked. If they had blocked it all of the site would be inaccessible.
This is something else, trust me.
As for actually doing work... god forbid that LOL
If I was not doing my job well I would be in the streets. My boss is quite nice and lets us play around during breaks and lunch hour.
I'm touched by all of your concerns.