Skype has expanded the capacity of group calls to 50 people and has added a notification feature for such calls. It started testing both features last month, and they'll be live for everyone starting today. The larger conference call option is a smart, if somewhat inevitable move, given that some other video calling services can host bigger groups than Skype's previous limit of 25.
Meanwhile, notifications will take over from ringing as the default for group calls, so prompts to join them should be a touch less obtrusive. You can still ring people individually or the entire group (as long as there are fewer than 25 people invited to a call) if they dally and a notification isn't quite enough to get them to join.