To try not to draw too much vitriol from the admins, I'd like to say first of all that I do like vBulletin. On the whole I think I prefer it to phpBB, which it certainly seems to have some similarities with in terms of presentation.
Linear - Oldest first
Ok for threads with only a few posts. But if message #187 is a reply to message #45 it's a bugger. Continuity suffers.
Linear - Newest first
Been trying that one out over the last few days but reading a thread backwards is only useful if you've been following a thread and there's an occasional post. No use for "discovering" a thread that has a lot of posts already. I'm an old time usenet user and so I hate top posting, which this mode is reminiscent of.
Threaded
I expected this mode to be the dogs nads, and it's the best one, but there are a couple of annoyances. IMO it would be cool if the height of the frame with the threads in it were user configurable. Also, the message "
More replies below current depth..." or something is nice to know, but I sort of would expect to be able to _see_ these if I click that link. I know this is configurable by setting "Default Thread Age Cut Off", but it doesn't "enhance the user experience" much if you have to go in and out of your personal settings.
Hybrid
Not quite sure what's going on there. But I don't like it.