ArtRage requires the machine to be authorised for use ( by entering your registration key ). While it may be possible to run ArtRage from a memory stick and do this the first time it launches, you will then end up with your reg key on multiple machines, which increases the chance of the key being flagged as invalid, especially if someone else installs ArtRage on those machines at a later date.
The advantage of installing ArtRage, then uninstalling it when you're done, is that this will remove the key from the machine.
Regarding email notification, you can choose your subscription options in the user control panel 'Default thread subscription mode' 'Instant email notification' or 'daily email notification' etc. This will automatically subscribe you to threads you create / reply to.
We have this option off by default as we prefer allowing users to opt in rather than need to opt out of receiving messages from the forums ( especially if they find themselves unsure how to turn it off ), but let me know if I've misunderstood.