For one, any changes you make to the system, including configuration files
or changes you make to get it to do what you want, etc., will be lost any
time you have to reboot the OS.

I guess it's possible you can make you own bootable CD... but I don't really
see why. The only Pro you mentioned (viruses) is not much of a concern for
a linux system. At least that is what I have heard folks saying. I would
add to the pros that it is more secure when entering personal information in
browsers (in that you don't have to worry about the data being stored
permenantly on disk or in some browser cache). As other cons, there is
going to be a fairly significant loss in speed.