duh!!! of course the Big brother can see what your doing!!!
however depending on company policy, and the size of the company he may not have time to check on every user to see whether they are misbehaving!!! so for instance if your entering a restricted site or one whose contents are deemed inappropriate the proxy server will simply prevent you from entering the site and log the sites which your tried to gain access to.Unless he's/she's a serious admin in which case they'd attach a bot to the proxy which will page them evry time a user is being bad!!!. there is a way to bypass the proxy though( what can't be bypassed these days!!!) simply create your own virtual proxy using your ISP or use the hundreds scattered accross the internet, then simply connect to that website (which is not restricted) and type in the website you want to go to. However most admins will catch port tunnelling but then again if you can't get to the site u want from within the LAN, u might aswell just go to a dumb cybercafe!!!