You're talking about casual surfing, right? I don't buy into the "moral relativity" arguement. Whether I choose to do the right thing is beside the point, in some cases, right is right, and wrong is wrong.

I would guess the only way to solve the "ethical" question would be to find out what the company policy is on it, and if there is none, to ask for a clarification. If the company says no, then it is stealing; if the company says yes, then it isn't. Pretty black and white, actually; it's their time , and their equipment, and you're obligated to use both as they expect - even if you're on a break.

Once the policy is made clear, if you choose to go against policy, and get away with it because it would be too much touble to enforce and "everyone does it," then you're stealing.

If, on the other hand, they say "it's ok, but don't abuse the privilage," then you're in a gray area where they can choose to make it an issue if they want; you would need further clarification in order to surf safely. If that were the case for me, then I'd strictly limit my surfing to breaks and lunch; the liabilities aren't worth the leisure.

Oh, and if you're just checking your email, remember that they can monitor everything you look at, and even the headings of unopened mail can say things that you don't want public. Not to mention there's also keystroke recorders that will store everything you type, including all the passwords you use to access things like email accounts and bank accounts. Do you really want to give them that kind of information?