I've been using Golden Hill Software's CloudPull Premium ($15 now, I only paid 410 due to a promo, TidBITS users can jump get a 20% discount if they insist) for a month or so. It backs up parts of the Google data associated with 3 of my Google identities -- Personal, Public (firstname.lastname@example.org) and Work. Sooner or later I'll start backing up the kids stuff too.
The backup data includes my Google Calendars (primary and subscription/shared as .ics), Google Contacts (3,496 as .vcf), Drive files (Google versions converted to iWork, else native) and Reader subscriptions, starred, shared and liked (not sure of format, seems a mix of database and references). The repositories are searchable through CloudPull and, since I changed the store setting to be in my Documents folder, via Spotlight. I don't backup my email accounts; those are in Mail.app.
The app seems to work very well. It's designed to backup every 1 to 24 hours, but I just run it every few weeks. It would be nice to have a once weekly or once monthly backup option, or to be able to schedule backups for the wee hours of the morning. I don't backup
My archive includes about 40,000 Google Reader shared articles, a SQLite database of about 400MB and total storage of about 5 GB. Not trivial, but manageable. The storage architecture makes use of SQLite and many shortcut links.
I am quite fond of this app. It has a minor glitch in an early version, the developer fixed that quickly. Highly recommended for every Mac user of Google products.