I am obsessive with unanswered emails in my inbox. They will always get answered cuz fortunately for the webmasters, I have no life
Holidays, weekends, late at night... But I have to say, that if you really need something answered and it's crucial, an email is much better than an icq... maybe just do both. Because I know when I'm using trillian or something.. if I lose my cable connection even for a minute, I lose all my screens. So that's a situation where someone can slip through the cracks so to speak.