Great work, but you need to make this more aware of vBulletin's NOPARSE bbCode.
I've noticed from your example page that you don't seem to be aware of it either. (You've got spaces in your example bbcode to avoid parsing instead). If you wrap code in [noparse][/noparse] tags then vBulletin will not parse any bbCode commands inside them. This was added in 3.5.x and up. It's VERY handy for showing examples to your forum members!
I've noticed (when citing examples for the members of my forum) that if you wrap your bbcode (gvideo] or [youtube] in noparse tags, and you have a Youtube or Google URL inside, the Google Video or Youtube document id will still be parsed out of it and displayed instead of the entire URL.
so for example:
[noparse][youtube]http://www.youtube.com/watch?v=XhgVIbO83o4[/youtube][/noparse]
will actually display
[noparse][youtube]XhgVIbO83o4[/youtube][/noparse]