I've been using VaultWiki happily since 2008. What I haven't been doing is upgrading, because I'm afraid the styling will go horribly wrong and custom buttons - or worse - will be lost. Since my installation's part of a paid-for service, I really don't want to find myself explaining to users why I just broke their wiki.
Suggestion: a reasonably-priced upgrade service, guaranteed to preserve the look and feel of a Wiki already installed and in-use.