Yes I understand what secure/private means quite well, thank you. Most folks do not. And sending anything off to the Cloud is NOT. I quite successfully sent Truecrypt'ed files to my lawyer, and he opened them easily with the software already on the CD; and he is NOT a techie. My clear instructions and set of files is all one needs.
You don't send a self-extracting .exe, that gets flagged by the System and A/V for sure (but should still be OK after a scan). Send a file with no extension. Truecrypt let's you manually browse to the file. If an accountant can't follow simple directions, I'd seriously consider getting a new one.
Another advantage of sending encrypted files, is that if the accountant leaves the CD lying around, it still does nobody any good because they don't have the decryption key.
Bottom line: If you are sending your SS # and other such info to ANYONE you are not familiar-with in an un-encrypted manner, along with personal financial information, your are taking risks I would never be comfortable with. But it's your identity, not mine. Do as you please. Convenience will be most people's Achilles' Heel. The 1-2 hours of extra effort to perhaps drive somewhere and hand-deliver a package is inconvenient. But its' nothing compared to the 1-2 years to get our from under an Identity Theft.
I most certainly do build my own PC's from retail parts and software. No crapware, no OEM-hobbled boards. Performance: outstanding.
If the NSA wants to get at my machines, neither you nor I will stop them. But with proper personal security practices, NAT-router, software Firewall, and A/V, I'm at least doing my due diligence to discourage the "easy-pickens" black-hats.