Personally I don't like offline mode, but do see its use (Login servers down? Offline mode. I actually run my dev server in offline mode because the damned login server kept going down when I was working on plugins).
What I don't understand is people who run live servers in offline mode. By doing so, really you are telling people that you support pirated copies of the game, because there's not really any other reason to run a dedicated server in offline mode (That I can think of, at least).
I'll admit, before I bought the game I pirated it, but I never dreamed of playing online, and I wouldn't expect any respectable server to run a server that pirated clients can play on.