IT admins are in their ivory towers reading everyones private emails. When they are not they are annoying and not doing their job. As such most of the comments are dont do it so they can have something to do during the day (like read your personal emails).
The expectation that someone will not check a personal email for 5 minutes a day at work is silly. No one lives in a silo while working. Except for IT guys of course. One aside, Euro zone privacy laws which are more progressive understand this practicality and enforce this reality.
I personally think the portable apps solution on a drive is the most practical. What I have not heard mentioned is using an encrypted proxy service like tor or ipredator. This will make sure the IT guys aren't reading about your dinner plans if you are using the office network.