Here's the thing - everyone loves karaoke but no one likes acting like an asshole in front of a bunch of strangers. XO is awesome because you can rent a room suitable to the number people you pour in with after the bars stop serving. It can be pretty pricey but sometimes you just have to belt out some Hilary Duff or Aqua without anyone passing judgement on you.
The song selection is pretty current and decent, but you should know that it varies from room to room. It took me a few trips to XO to realize this. Some rooms have kind of a lame selection, especially compared to some of the larger rooms. Also, you'll be irritated when the room you're in has the WORST and LEAST RECOGNIZABLE songs from your favourite artists. It's really odd.
And drinkers be warned: if you order about 17 beers at last call employees WILL come in and clear them all out moments later. This has happened to me on a couple of occasions. You assume that as long as you've bought them and you're in a private room that they will let you guzzle them all down. Not the case.
Again, it's pricey but if you go with a group amped on singalongs then it's a wicked time.