I second the guy who voted for Jungledisk (and S3). It might not be as cheap (in theory) as an "all-you-can-eat" plan, but $0.15 per GB stored per month (plus bandwidth) is still cheap, and you get network drive support, block level uploads, user defined encryption keys, yada yada yada. AND I'd rather trust my data to Amazon, frankly (who copy it across multiple geographically remote sites). My experience with some of these "all you can eat" operations was great right up until I wanted to restore some lost data, then the *really* slow response times (still waiting after days) got my goat and I thought - "hey you gets what you pays for here..."
Oh, and Jungledisk does Windows, Max OS and Linux (all included for the one price).
And no, I'm not linked to them, just a very happy customer.