Just to add to SPF Q&A here: it's not something you can turn on easily. It's very easy to mis-configure it and therefore takes a lot of planning, especially in an organization with a highly complex email strategy such as Zen's (great ISP choice btw, they WILL talk to you about SPF if you ask).
Back to your original query, BOAC: did you download the software from the vendors' own web sites? I have done countless downloads of Skype and iTunes and never seen my email address misused. Just out of interest, you don't need to enter an email address to d/l iTunes
