What if a Web service could pull your old e-mails from those services you don’t use anymore, and combine them with an archive of your current e-mail? So no matter how many times you switched e-mail providers, you always kept your information.

Imagine it worked the same way with your address book, plopping your contacts into Outlook on whatever new PC or phone you bought.

Now imagine it could also store all of your photos, documents and videos, and make them accessible from just about any device with an Internet connection.

I think something like this is on the brink of happening in the next two years, and not necessarily because Google’s (GOOG) going to do it; a startup called Sharpcast has already taken the first steps. I also think such technology could bring consumers valuable leverage, and provide us a much-needed safety net as we move more of our data online.

That is, if Sharpcast blossoms, and has the courage not to ink the wrong kinds of deals with wireless carriers, ISPs and other subscription-hungry companies that want to use our data to hold us hostage.

I had a chat on Wednesday with Sharpcast CEO Gibu Thomas (pictured above), at a Starbucks down the block from the Web 2.0 conference in San Francisco. As he demonstrated Sharpcast’s photo-syncing app – it lets you see your photos from any Internet-capable device regardless of whether it’s connected at the time, and share photos with others – I started to get the same feeling I got five years ago when Apple Computer unveiled the iPod and put one in my hands.

I’ve used something like this before, but it didn’t work right. This works right, and it could change everything.

Gibu explained some of the technical details behind Sharpcast’s server-based technology, and demonstrated Sharpcast automatically keeping a Word document and Outlook contacts in sync across a cell phone, two different laptops and a Web browser, without him pushing a bunch of “sync” buttons.

And it hit me. What Sharpcast has created is the beginning of an online treasure chest that houses all of your valuable data, and allows you to access it from any device using a single sign-on.

An online treasure chest like that is potentially very powerful, especially once enough people have signed up for it. It could allow people to more quickly and easily upgrade their computers or cell phones, take advantage of new technology, and ditch service providers that don’t remain attentive to the customer experience.

In fact, in a world where we increasingly have multiple PCs and mobile devices, all of which can break or become obsolete, one could argue that we need a sync app like this, for insurance as well as convenience. So here’s hoping that something like Sharpcast indeed fulfills the technology’s potential. And soon.