For the ones that store information in a local file, that could work. But then a lot of the mobility is lost, even if you use something like Dropbox (you are not going to sync behind a corporate firewall, for instance). At least my brain is attached to my head and is very portable, I just have to remember the damn things.
That said, do you have recommendations?
The one thing I'm waiting for is iCloud integration. If they don't provide iCloud integration, I'd consider other options (including trying to roll-your-own, maybe using their extensions and spoofing the IPC)
Edit: Here's a link (no ads or other junk). http://16s.us/sha1_pass/