Disks, hard drives and computers were seized as a part of the operation, and even though the compound did not have a (wired?) Internet connection or phone lines, the data on these media are, of course, potentially extremely valuable to US intelligence.
al-Quaeda has been known to use encryption before, so it’s not entirely sure that the plethora of digital forensics experts (that are beyond all doubt hammering the disks with all their skills as I write) will come up with anything useful – nor is it certain that the disks contains any useful data at all. Maybe old Osama just fancied playing minesweeper.
Even if encryption is in use, it’s still a question of what kind of encryption that are utilized, where it is utilized and how it is utilized.
What kind of encryption: Weak encryption has been used before, and there’s plenty of examples of XOR-ciphers being touted as “military grade encryption”. A strong encryption scheme uses a scrutinized encryption algorithm (like AES, RSA, Serpent, Twofish, etc.) that are correctly implemented, with a secure key bit length.
Where it is utilized: Encryption can be used to protect data, but it is up to the user to select what data he/she wants to protect. You can choose to encrypt files, partitions, disks, whatever that contains data. Depending on the selection, copies sensitive data may reside on unencrypted files, partitions, swap space, other disks or other media.
How it is utilized: There’s plenty of examples of users choosing bad passwords or otherwise compromise their encryption scheme by using it incorrectly. One prime example is letting a computer that utlilized Full Disk Encryption (FDE) being seized while it’s powered on or in standby mode, potentially allowing access to the data.
Nevertheless, the weakest link in encryption cases are often the password. Time will show if Bin Laden was as careful with his data as he was with his own physical protection.