http://www.spideroak.com is nice but unfortunately they started to implement some file sharing features so they stopped offering true client-side encryption as well. At least they are way more secure than DropBox. Another one: https://secure.cloudsafe.com/
1) "Second: the security economics of mail drastically favor Google over anything you come up with, even if you're really good. That's because the cost of a sitewide compromise at Google is stratospheric."
This cannot be a serious answer: Some chinese already compromised Google a few months go - they stole the "Gaia" source code. Gaia is the single-sign-on solution for all Google services! Just because they are not unsing it on a big scale you can be sure there are people using exploits found from the source code to log into Google accounts.
2) "People who care about mail security but don't trust Google just VPN to a private mail server."
A VPN in general can be considered secure. If configured properly. Same for a mail server and for the network behind the VPN. In general: I would recommend a secure file sharing environment focussed on security & encryption. And no, that´s not Dropbox or box.net.
There is no better solution than GnuPG/PGP client encryption. Or at least partially secured file sharing offers like datainherit.com or cloudsafe.com
And I would -not- recommend DropBox for critical backup files. First, they can read all content. Second, they got some problems with large folders or system directories.
Even if you work alone - make sure you keep touch with your friends. And make sure you get a network of business contacts to talk to, people from your part of the tech world.
It´s not only important to keep morale up, it´s also important to get other people's feedback early stage!
there are THOUSANDS of site offering this product. Do you research your ideas before you post them? :) Still, there could be a search site just for all the checklist sites... (!)
Dropbox. Well, it´s an online and offline solution for me and my most valuable files no a Macbook Pro - since I get online access via getdropbox.com and I got an old PC (yes, a Windows XP PC) as a sync client for Dropbox on a second location. So if both machines fail: Online copy. And if Dropbox fails, I still got everything on two harddisks in separate locations.