I currently use Vbulletin for all of my message boards, but absolutely love the ideas behind vanilla. That said, some of my forums are pretty busy and I worry about performance. Are there any large scale installations of Vanilla anywhere?
And I realize "busy" is relative, so:
An average forum of mine has about 10,000 users, 1 million posts, and 450 people online at a time...
Further to that end (seems to be marks word of the week?), there are people on here who have installed it on forums of what i would consider to be very large (i think they were talking similar figures), and after some tweaking with mark (which are now core, i think) were very pleasantly surprised with the performance. You can correct me if i'm wrong, but vBulletin isnt considered one of the fastest softwares out there is it? Compared to the likes of punBB (seems to be highly regarded speed wise), etc..?
Speed is really only relative to what you're running under, however, Vanilla should be fairly scalable as it is with room for improvements. So if you want, do a side-by-side comparison, and yell back here with any issues that crop up while you're running and someone will be more than curious to try to help you out if mark doesn't first.