*IT Manager alert*
A lot of the filtering will not be done by any one checking or changing settings, site categorisations are down loaded by the filters, and unless your IT staff don't have any other work to do, they probably won't be checking what you're up to.
We have one site with seriously limited bandwidth (4mb supporting about 120 users) so have to protect that as best we can, quick check of the high bandwidth users and what time of day it's at so see if someone needs a talking to.
The blocking of email is generally try to prevent data leakage (as well as making sure people do some work) we've had instances of people sending data out through personal web mail, hence it's now blocked, as well as logging what is done with USB devices, and archiving all internal mail.
Again, never have the time to look at what's going on (not that you can legally look through anyone elses mail) but does proove useful for prooving when someone's using the company for criminal activity.
There's also the issue of whether your company has a PRS license if you're listening to music (and who else can hear it)
It's a bloody mine field, i tell thee!!
*/IT Manager alert*