Good for a new site, not for existing ones
 

How to loose members? It's simple answer, just upgrade your vbulletin 3 o 4 to this new piece of s.. ..oftware.
How to fear members? The answer is the same as above.

Only if you consider to start a completely new website you can install this vb 5, because this is not a forum software (or it doesn't seem). I perfectly know that every innovation can alarm people (= us, webmasters), but our scope is to offer the best web experience to our users, and to dramatically change things is not what we want to.
That sayed, I personally never upgrade to it if it continues to look so different from a forum.