This feels like a better place to discuss my feelings on it as they are right now:
I've only been on vbulletin since 4.0 came out. It was HELL trying to convert wordpress/phpbb/mediawiki/drupal (drupal for my file sharing database) all over to a single platform... but it was worth it. I've got everything running under vbulletin and even just picked up this fancy new theme from dragonbyte. However, while working on that massive website conversion (I started in February of 2010 and switched over in August of that year) I watched a lot of people running mods under vbulletin 3.x who were waiting or having to use half-assed solutions to convert their sites, or be forced to stick with outdated software. Even larger modifications, like vbseo appeared to take a very long time to update.
Since then, I've seen things like that Xenforo thing pop up, and lots of modification developers jumping ship (or claim they are) and some working on both (like dbtech and the makers of vaultwiki). I've also seen times like this latest 4.2 release of vbulletin where one MAJOR change was implemented to screw up a lot of modifications without an apparent reason for it (the vbulletin navbar system annoys the crap out of me, before and after the update).
My biggest worry now, if vbulletin really is going to release 5.0 by the end of the year, is what will happen with my site. Will there ever be a 4.3, 4.4, etc for vbulletin? Fortunately most of my modifications are from dbtech, with the main exceptions being DownloadsII, Vaultwiki and vbseo, but I'm already worried about having to do another ridiculously large update. I wasn't around for the 3.x to 4.0 switch, so did most paid modifications require paying for new versions?.
Mostly, I feel like I don't want to have to do another big project so soon. I can predict what would happen if I tried to update: I would break all my caching, many URLs would have to change, I'd lose some functionality somewhere and have new functionality elsewhere that no one knows how to use yet.
Oh, and the whole "modules" thing mentioned in those screenshots, they remind me TOO MUCH of drupal. I never want to touch drupal again. Drupal can die and go get lost in the interwebs forever.
Anyone else less than happy about this vbulletin 5 announcement?