For the record, the SDL does talk about encryption of PII data (like documents). Consequently SkyDrive will almost certainly be strongly encrypting data when sending the data to and from SkyDrive, and all data will be stored in Microsoft's hardened data-centres (i.e. you're not going to find a SQL injection against the SkyDrive website).
SkyDrive probably won't be meaningfully encrypting data once it's in the cloud (i.e. if they do encrypt it, Microsoft also has the key to decrypt it) because otherwise if all of your laptops failed you'd never be able to get at your SkyDrive data again.
Also, if you're using Microsoft Office to store your bank statements and documents, you can apply a password to it. Doing so strongly encrypts the document, so that even though SkyDrive can see your document at rest, it's at-rest form is still encrypted using your password.