Not that I will be switching to it immediately, but Copy.com might be a contender. I'm somewhat partial to it because, unlike many of these services, it isn't a startup of unknown staying power but rather a subsidiary of a pretty large, successful company (Barracuda).

Hello, Doug.

Thank you for asking.  Our apps will work sync via any file syncing service that will sync arbitrary files, although to work efficiently, the service must use smart incremental syncing of files.  If they don't use smart incremental syncing,  they are going to up/download all of your bookmarks (typically several MB) any time you add or change a single bookmark, which could get annoying.

• Google Drive.  I'm not sure if they do smart incremental syncing.  I shall test it and get back to you here tomorrow.

• iCloud Drive.  As far as I know, iCloud Drive is not available unless you're running the Yosemite Developer Preview, and we have other issues with Yosemite right now.  The current version of iCloud, available in the Lions and Mavericks, does not support syncing of arbitrary files, unless you use the Mobile Documents hack, which I don't recommend because iCloud Drive will be here soon.

Dropbox has met both of our requirements since day one, which is why we've always recommended it.  But I know Dropbox has fallen out of favor with many users recently.  So we need to retest some of these other services and update our list.  Microsoft OneDrive is certainly a candidate; there are lots of others - SugarSync, Wuala, Memopal, etc.  Let us know if there are other services you'd like us to test.