1. Secret Sync – this is an add-on that encrypts files on your computer, using a key that nobody at Dropbox has, so even if someone gets into your Dropbox account, they can’t read your files. It’s free, but they plan to roll out a “pro” model with additional features.
2. Spider Oak offers client-side encryption built in, so it’s essentially the same as Dropbox + Secret Sync and is, like Dropbox, free for 2GB.

Secret Sync (or actually, I think it’s SecretSync as one word), being a different company entirely from Dropbox, means that your DB and SS passwords are not shared between companies, so that should be as secure as your passwords.

Spider Oak is one company, but they claim a higher level of privacy than Dropbox:

At SpiderOak we have created a true ‘zero-knowledge environment’ meaning that no one including the SpiderOak employees will ever know what you are storing on your SpiderOak Network. We can maintain this environment because at no time will anybody know your password (or the answer to your password hint) except you.

I still haven’t decided whether to switch. I’m pretty pissed off at Dropbox for the misleading statements they make on their site (saying all files are AES 256 encrypted – essentially unbreakable – but neglecting to say that they have the keys and with certain forms of attack the hackers could have them too!). Still, one of the things about Dropbox is it is very bandwidth efficient and I am bandwidth limited because I’m often connected over satellite. Dropbox tries to upload just the pieces of a file that have changed (based on filesystem sectors?) and to not even upload common files that a lot of people share (very popular songs). Once you switch to full encryption, I would think that changing a single period in a document would result in a completely different encrypted file, like if you were doing a hash, and require a full upload.

Spider Oak says no:

SpiderOak will scan the file and find only the changes, and store new data blocks for those areas of the file. This means that SpiderOak is able to store all historical versions of a document using little additional space.

For example, if you’re working on a research paper, and add new sections, charts, and other information to it as you go along, SpiderOak just stores these additional items. So, SpiderOak will be able to store all of the historical versions of your research paper using about the same amount of space as would be needed to only store the most recent version.

So it would probably be worth it to switch, but we turtles don’t do anything fast!

Not bad. They tout all over that it’s “totally free”, which it is – it’s Ad Supported. I don’t necessarily have a problem with that, but there’s adware and there’s adware. In other words, Opera and Eudora were long ad-supported and all they did was show ads at the top of the application while you were using it. That’s fine with me and more or less like visiting a website with banner ads. You have to pay for stuff somehow. As long as it doesn’t install some ad server on my computer that runs in the background whether I’m actively using their product or not, I don’t mind (though I might like the option of paying a reasonable fee to upgrade to paid, ad-free version).

A bit more looking and I came across a bunch of other VPN clients and settles on Security KISS which is free if you keep usage to reasonable levels and works fine, but of course adding in this proxy and encryption will slow things down a fair bit.

Anyway, if you’ve tried it and have any info on what sort of ads it runs, I’d much appreciate it!

[update]
Okay, I did a bit more poking around and it looks legit.

• PC Magazine lists it among their five favorite free security tools in 2008.
• I looked around the anchor free site and it seems that the way they work is that by going through their platform, it allows advertisers to place ads on wifi hotspot login screens and on websites themselves. Basically, they have signup forums for both wifi providers and site publishers to opt in to running ads associated with their platform and then presumably they have a way for advertisers to put their stock on selected websites. For example, the page for web publishers says:
  

  Join thousands of premium web sites who are earning from AnchorFree’s patented technology that touches our in-transit audience…. Allow us to place contextually relevant advertising directly on your site to earn incremental revenue attributed to our multi-channel platform.

  So essentially, it’s similar to Google ads. Actually, a clever business model if I understand it correctly.

Anyway, it seems all relatively open and legitimate and definitely worth a few ads for the peace of mind it would give me when on an unsecured network. I’ll try it I think, but I would still really appreciate a comment from someone who can verify whether or not it will show popup ads on my computer or silly things like that.