On Thursday, May 28th, Linden Lab announced that with immediate effect, Premium Members can now join up to 60 groups – raising the limit for them from the previous 42.
This increase is only, for now, a pilot programme, for reasons explained below. However, all things being equal, it will hopefully become a fixture of the Premium account package.
The news came via an official blog post, which reads in part:
Today we’re thrilled to be rolling out another perk for Premium members: now you can be a member of 60 groups! Groups have been a consistently popular feature among the Residents of Second Life. It may not be obvious, but group membership can have an impact on the performance of a number of systems. That’s why in Second Life’s early days, Residents could only join a maximum of 10 groups. Over the years, we’ve made improvements that enabled us to raise the group limit to a maximum of 42, but we know that for some power users, even that isn’t quite enough, and today we’re happy to raise the bar for Premium subscribers. We must make sure that the recent gains in group performance are not jeopardized, so for now the new limit is a pilot program. If there are no problems, we will look forward to raising the limit further (stay tuned!).

The “gains in group performance” referred to in the quote above are related to the recent improvements made to the Group Chat service. These have been going on for almost a year now, spearheaded by Simon Linden, who has been working hard to bring about significant improvements to the entire group chat service, front-to-back.
One of the key aspects of these changes relates to how various “update” messages, created every time someone logged-in or out of SL, etc., and which required updates to be sent to every group of which they were a member, could actually interfere with the group chat system sending and displaying actually messages being members.
At the time Simon was working on these changes, it was indicated that the Lab might consider raising the limit on the number of groups people can join if the work proved successful – so kudos to Simon here for all his hard work – and kudos as well, to the Lab for approaching things cautiously, and recognising that should the new limit prove detrimental to the performance gains that have been achieved with group chat, they are prepared to roll them back.
There is also news in the post for those who take advantage of the increase in the group limit, and then subsequently opt to downgrade their membership to Basic:
Premium members can immediately take advantage of the new limit. Downgrading from Premium membership will not remove you from any of your groups, but it will mean that you cannot join any new groups until you remove yourself from enough groups to get below the Basic account limit, which remains at 42.
This is a further change to the Premium account package that sees things continue to pivot away from the idea of quarterly “gifts” and the like, and towards offering options and abilities that users are more likely to find of use and thus appreciate more. Again, as the official blog post states, expect further updates to the Premium account offering that continue to move in this direction.