Google Cloud Storage provides gsutil rsync, which is helpful for uploading large folders. Bonus points for checksumming.
Edit: I hear that HashBackup provides rsync capabilities with b2.
Appreciate the feedback and we'll take a look at that rsync utility. We're also working on a simple client app that will do rsync with B2.
We're also starting to work with partners to offer a variety of other integrations. Duplicity and HashBackup have integrated B2, and Duplicati has an early alpha version. Someone is working on a FUSE integration. So hopefully soon there will be many ways to use B2. We'll list them here: https://www.backblaze.net/b2/docs/integrations.html
Please keep sharing feedback of what you need and how you'd use it!
Gleb from Backblaze
For people on a slow connection, rsync plus cheap storage is going to be a really big deal. Here's hoping it happens!