Great idea. I have some feedback.

When I land on the page, there's no clear place to look. I should have a clear, linear path that explains what the site does and then invites me to register. Instead, the first thing I see is the invite-a-friend button, and then some useless information about a new release, then the feedback button, a beta button, and finally, sign in.

Then, when I'm wondering "what is this place?", I see some marketing speak.

Rather than "no matter how many accounts, it's one place to keep them synced," with random bolded letters, it might be better to say "tell us what social applications you use, and we'll import your information. when you change your atomkeep profile, and all of your other profiles will be
automatically updated, too."

The site is filled with lots of marketing speak. For example, "Atomkeep is here to solve the problem of information redundancy." is itself redundant when you explain the function of the site-- it's very obvious what it solves.

A great idea, though. But simplify and explain functionality and benefit.

Also, your incredibly refined help section seems kind of silly when the site is so simple. If you explain everything cleanly in the beginning, why would anyone need to click help (also, they never click help; they just close the page)?

--edit--

I also want to mention that the register form, while clever, made me not sign up. I am sure that after I enter my email address, you'll send me some email and I'll eventually have to pick a password somewhere. The uncertainty of where I would be choosing that password made me not sign up. One aspect of being polite to your users is making sure they know what will happen when they do something.

--edit--edit--

Curious, I signed up, and was prompted to enter a password in a javascript modal box, the one thing I hadn't even thought of as a possibility. After entering a password, I was presented with this, which reminded me so much of average UI on the web today that I felt I should critique it:

"We've sent a confirmation letter to your e-mail address me@dustincurtis.com. Please, click the link from the confirmation letter to activate your account. If you would not activate your account within 48 hours from the date of registration, your account would be permanently removed. Thank you.If you didn't receive the confirmation letter, please, check your SPAM filters and folders. If you still experience problems activating your account, don't hesitate to contact us."

This is not a polite thing to say to your users. It uses negative, commanding tone, issues a time limit, and then says that if I refuse to do X, my Y will be "PERMANENTLY REMOVED." For this application, I would assume that 90% of your users are used to how the web works. In that case, I suggest you change this huge paragraph to something like:

"Thanks for signing up. We've sent you a confirmation email you can use to login."

You don't need to mention the part about the spam folder, because people who would use this service will probably know about that already. Also, "If you still experience problems activating your account, don't hesitate to contact us," adds no value; if I have problems, of course I'll contact you. Most likely, though, anyone would just leave.