I booked Ribon for my 30th this weekend and had an excellent night, so I wanted to make sure there's a review on here for them. Other sites already have good reviews, and I'd been to Ribon a few years back, so I was expecting a good night and wasn't dissapointed.
We had the downstairs room, which was great for a large group. There were around 40 of us, but from 30+ would be fine. The food was excellent - they'll serve it seating or buffet style, it's up to you.
Staff all extremely friendly and attentive without getting in the way. There are swankier places to do karaoke in London, but they're often well overpriced (and a bit of dated decor add's to the atmosphere).
Excellent value, excellent food, top night out.