The Charles Playhouse Lounge has been closed for renovations for months. But they've recently re-opened! In my opinion this is one of the best spots in town for karaoke (though after the remodel it's a bit bright and cafeteria like in there...they'll fix it someday, I'm sure).
Karaoke usually starts around 10 or 10:30 though the bar can start filling up around 9:30. I'll try to get there early enough to grab a table.