Seat limit is a good idea Cow, but I can say that honestly if I use 3 this year, it'll be high. I've got one booked at Christmas because it's worth an extra $250 at least vs the fare/regular fare.
I can see though a couple family vacations with the way you guys need to route/book things some times that 10 could vanish quickly.
My issue is, it seems that any time I look for a booking, it basically has to be IKK. So if I booked 10 trips in a year, there's a good chance all 10 would be IKK.