I've stayed out of this for the most part but felt it time to chime in because I see this from both sides. I'm the one responsible for keeping track of where our resources go.
We use tools like WebSense (for logging not filtering), Scruitinizer (so see where our bandwidth is going), as well as other nefarious things to help keep our users on the straight and narrow.
(That's said with tongue in cheek).
Our environment here is very 'Open'. We don't restrict anything, but we do monitor. We monitor for a number of reasons:
1) Bandwidth, while it's never been cheaper still isn't free. We host our own stuff and do so proudly. We like for our 'Customers', the folks who are paramount in the Salary Continuation Program to have a good experience when the visit and download our software. Bad experiences because there isn't bandwidth to serve their needs is counter productive to the Salary Continuation Program.
Examples: We had a user bring in a Slingbox to 'watch TV at lunch' streaming his saved TV shows from home, sucking up considerable bandwidth, much more so than is advertised, and oh, it was non-stop, not just at lunch. This was not a good day (for him or us). March madness time, our bandwidth utilization usually goes nutz, even though we provide 3) large screen TV's for folks to mingle and watch their favorite schools play.
2) People, (not all, but most) are in inherently lazy, that coupled with doing something that you don't actually LOVE doing will drive them to do things that aren't necessarily core to their job. (QA testing is monotonous to say the least, and doing design/engineering work on a product that you don't actually love also sucks, but the work still has to get done). We watch for trends... People doing stuff out of the ordinary... If all of a sudden your non-business internet related activities jump out of bounds; you're bored, don't have enough to do, or something is wrong. We leave open the possibility that you're having a bad day, that **** happens, but if the trend continues we'll talk about that.
3) People, outside of being lazy, are often dumb. If you need proof, just go to YouTube. When people do dumb things it costs the company money, money that we'd all rather have paid to people like me and ultimately you the employee and/or spent on benefits like 100% paid medical, Foosball tables in the break room, etc, etc.
Outside of all the protection we have in place, people still find ways to break **** and bring viri into the organization. While this is generally contained, it's still expensive. Last week we lost two man-days restoring machines from backups from people who followed what they thought were links to NY-Times Articles that hosed their PC's. One IT guy, two full days to blow away and restore machines from tape. Two engineers down for almost an entire day each, simply because someone was dumb... But we realize **** happens too and you can't protect everyone from everything.
We all have our diversions, and we all need them. I'm posting this from work, and it's perfectly acceptable. Are there days it gets in the way of my work? Sure... But not usually to the extent that it's a problem. I stay later, and get **** done as is needed.
More importantly we monitor to cover our *****. In this crazy litigious society we live in. We have to keep tabs on what's going on in our work place. From Copyright infringement, to someone with a gambling problem who works in finance, to someone searching for a way to off their spouse. You'd be amazed at what people will do at work that some wouldn't do at their own home.
[Ramble OFF]
[Note much Sarcasm mixed in]