If you're a Mac user and you're using the NEO tokens as smartcards for ssh authentication, you may want to refrain from "upgrading" to 10.10, due to this issue:
http://support.gpgtools.org/discussions ... agent-modeBasically, your ssh sessions may get stuck in authentication, randomly. Or authentication may fail, as if you're not using the right ssh key.
What seems to be a workable temporary fix is to run "pkill gpg-agent" a few times, then manually do "gpg-agent --daemon" once, in a terminal. Sometimes you may have to unplug / replug the NEO token, too. That usually fixes your ssh authentication with the NEO token.
OS X 10.9 seems to work just fine.
For context, this is a setup similar to the one described and discussed in this thread:
[HOW-TO] - Yubikey NEO, OpenPGP, OpenSSH authentication