Recently, I bought an Invision Power Board License. To test with, more than anything, however, I am now thinking of actually using the software on a live forum.
Alot of the IPB admin control panel is confusing to me, as a devout vBulletin user alot of IPB is foreign to me, whereas I am very familiar with vB, having released several mods and providing professional vBulletin Services and other such things for it.
However, IPB from a user standpoint is quite friendly, some of the skins for it are very professionally done and don't look simply like recolours, to licensed customers they even offer several services, such as the Skin Generator and the free IP.Links and IP.Shoutbox applications. The attitude toward customers is also very refreshing, with the guys at the top fighting over my support ticket, always nice to feel loved guys, lol.
With all the new features in the upcoming IPB 3.1 release, IPB is looking more and more exciting by the day, the status updates feature has always been good, but they have improved even that in the new release, and the twitter connect functionality is pretty awesome also.
I haven't yet looked into the Plugins side of IPB, you know, developing and such for it, but I have looked into the templating system, when I first saw it I thought, "oh god, not vB4 stylevars all over again" - but its really just a tabbed template system, each template opens in a new tab in the same window, if that makes any sense, which, again, is refreshing, in even vB3.8 - you have to go back through templates, save, open a new one, save, open, save. It gets very repetitive and boring, so that was a nice change.
To be honest, I am looking forward to more 'refreshing changes' but I don't think I will be ditching vBulletin any time soon, I may invest in IPB more though. Who knows what the future holds.