Thomas,
The reality is that ANY time on ANY network or system you use, there are people that can or do collect information on your usage of that system. Generally this will be something as innocuous as a logged event for when you authenticate or connect to the system, but it could be a full capture of all the activity you undertake - such as that can be done using Wireshark/Ethereal, and which you are referring to. If it is for the purpose of administering or managing the system/network then generally this is legal - provided that they treat that information within the laws governing privacy that are appropriate. (For instance, if they do record your IP address and login name, they need to sure make this is not available to the general public - or even to people in their own organisation that might not have a need for this information). Of course if the purpose of capturing that data is for something other than managing the system/network, and might infringe on your privacy, then they are probably breaking the normal wiretapping laws that are appropriate.
So in summary, people can and do capture information about what you do on systems you use. Therefore be aware of this, assess the risk (to your privacy) and act appropriately.
Of course I am not a lawyer (and have no other detailed law enforcement knowledge), so treat this purely as the opinion of technical guy.
Regards, Martin
MartinVisser99@xxxxxxxxx