So. iDrive is $15/month for 500GB. You can backup multiple computers (but not both PC's and Mac's on the same account). And it doesn't automatically delete data after a set period of time. Right now I have two iDrive accounts (one for PC and one for Mac).
Sugarsync is $15/month for 100GB. But the interface is a tad more clear. Its purpose is different too -- it's great at syncing files and folders across multiple computers (and platforms.) So I use the free version to essentially backup my documents.
And that's how it is.