Even if you are happy that every file you have complies with Microsoft's Orwellian policies, it seems like far too big a risk to take that their systems might flag something innocent (how many ordinary magazines and newpapers contain pictures with "parital nudity"?). When the punishment is losing not only use of Skydrive and whatever files you've stored there, but also your xbox live account, hotmail account and everything you've bought for WP7 if you were mad enough to buy that, it's not something I'd risk for the sake of a bit of storage. The advantage of Dropbox is if they cut you off for whatever reason, Dropbox is all you lose.
For backups I use Crashplan. It's in the same ballpark of backup services as Carbonite, but has no storage limit and the software is more flexible. You should be aware that even with a fast ADSL connection, it could take months to complete a full backup to a remote location, depending on how many files you have. The nice thing about Crashplan is that it's a full backup solution for local external harddrives and you can even back up one machine to another if you have a faster local connection so you can get a backup done quickly to give a decent piece of mind while you're waiting for the remote backup to complete. Encryption is available up to 256 bit and performed locally. You can select an option so that it never transmits the encryption key to Crashplan's servers, but you'll lose browser-based access to your archives if you select that.