PCWorld.ca has an article today that tells 7 things your company's IT department doesn't want you to know which technically I agree most of them. And it's true that with so many useful awesome online applications out there it's nearly impossible for IT department to restrict their employees' use of work PCs and networks to lock down the system and compliant with their policy. However, spreading words like this on a popular site like PCWorld makes our life way much harder, which is why I don't include the link here.
It's always true that the most threat to the network are from inside the office. While it's hard to technically lock system down it would be more efficient and useful to have a more strict and seriously detailed policy in place. And be sure that the words about the policy get to people's attention.
[updated on Jan 11, 2008] Apparently, people in PCWorld reviewed and realized the potential risk of this original post (note that I included the link here now) as it has been removed off the website but maybe still archived somewhere in their storage.