One of my workmates regularly accesses Facebook using a proxy, then deletes her browsing history at the end of the day. I'm pretty sure IT will still be able to see her internet activity, is that right?
In the last week or so, we had a mail about how access via proxies is definitely not allowed. Reading between the lines, I think someone may have been sacked for it.
As OutToGetYou says, they will see the proxy use, but not exactly what is accessed, which is why it's banned.
Deleting the browsing history will not make any difference - we log everything anyway, even if local history has gone, and traces can be set up if HR thinks there's a need. And it's really horrible, having to go through internet logs as part of an investigation to see what people have been doing.
Our policy allows limited personal use, but if it's causing problems with productivity, that will be taken up. All webmail has been blocked since someone introduced a virus that way. They've also introduced a really annoying policy of blocking any sites not already known, which you can request to have unblocked, but if you're searching for something then and there, it's really annoying to have to wait for it to be unblocked when you request it.
People do stream stuff like big sports events, but they've also been known to put them up on the big screens which are actually meant to show lists of problem tickets and the like.