Curious to see if others have their own suggestions. We've noticed that if we not pretty vigilant about it, the creep factor sets in and suddenly there are lots of weird things happening around micro-features.
Also, although I understand many folks have philosophical problems with this, you should support one-click log in with at least one of Facebook, Google, or Twitter. I almost certainly do not want to make a password for your site.
Consequently I don't think you can include brackets in your password if you want it to work. The front-end apparently isn't aware of this limitation, so they'll happily let you do it.
Code re-use: a very good idea.