[sean2]

I don't actually see the scenario where this becomes a problem.

If foo.com is compromised and their passwords decrypted, I find it unlikely that the attackers are going figure out your password scheme, go over to bar.com, and start trying out usernames that are similar to yours with the password scheme they think you have, while they are in possession of all the other foo.com passwords and usernames, some of whom probably have the exact same username and password on bar.com.

I've been using basically hunter2_foo for all unimportant passwords for some time and never had a problem.

The only thing I can think of is that if one person was on a mission to destroy my life and they managed to compromise a couple passwords to figure out the scheme, but I don't see that happening in a way that would not allow them to vacuum up a good number of passwords anyway.