Yeah it really is tempting to buy two additional licenses and even an extra year of upgrades for them. But it feels a bit like a dive in the unknown for me too. Not thinking of the lawsuit specifically although when investing a fair amount of money everything comes into play and feels like a risk. Need to think about this...
I don't care about the lawsuits.
I felt that vBulletin 3 would be fine for a few more years, without even considering version 4. And I was right. A lot of sites that I still like run on vB3, and do just fine. However, compared to XenForo it feels outdated.
XenForo had this stable feeling since the alpha, and the stable is out now. Even if it discontinues as a product it will be a more modern solution for me and my communities that I power with it, for a handful of years.
I strongly believe the framework allows for great add-ons to be developed quickly, and using sites where styles are made and xenfans and what not .. they will be easy to share as well. There's a strong enough community behind it to make something that's worth upgrading from vBulletin or IPB from, for me at least, for the next 24 months. And I believe that in 2011 there won't be an outcome in the negative towards XenForo Limited that affects customers or development, so that's about 6+ good months of maintenance and point releases, and in 2012 those 24 months start ..
A few years for me to run a fun community, sounds like a good hobby to me.
Things always change, we will see if that 'worst case scenario' even applies to customers, in what shape or form, and how that affects me running a hobby site.