I understand and I mostly agree (I refuse to get involved with store loyalty cards), but sometimes setting up an account can be a good thing. In Baen's case, it gets you access to books you've purchased in *all* the formats that are available (Switch ereaders, download new format. Hard disk crash, download a new copy). And in all the time I've purchased books from Baen, I've never received unsolicited email from Baen or from anybody else with my Baen specific username/email address.
You're willing to hand over your credit card information, but not willing to setup a username. (And yes, I know you mentioned Paypal, but there's problems with that path also). Neither path is totally secure in all cases. Setting up accounts (MobileRead for instance) provides additional privileges/benefits that can be worthwhile.
I've learned to be cautious, but not anal about my personal information. I've been online too long to worry about my email address being on some spammers list.
