PostNuke is coded a bit different than PHPNuke, but to use an analogy: PostNuke is your basic car, PhpNuke is your car with CD,DVD, LCD scrn, auto start alarm .. ect ... VBportal is a shell on VB that was ripped from PHPNuke and integrated into VB.
Vportal is cool if the forums is the main part of the site (security, add news, d/l, web links, section, etc ...) Like Josh said it is great for a quick install and poof all in easy.
But no its not "NUKE", there lacks in modual support, gui admin, simple template editing, quick theme swaping ... on and on (i started useing Nuke ver 4.1 w/ phpbb 1.3) the security to make admins to do jobs needs help.
EX. You can make an admin and give them access to editing NAV boxes, newsletter, faq, on a per modual level w/o giving them access as a full site admin.
It is a great product (vportal) I am useing it now w/ VB. Its current setup uses the color theme of VB and has sep templates to edit the look. I just have grown out of Vportal for my needs and with the Nuke / VB hack that adds the users to both platforms its time to start coding nuke front end and VB forums (the perfect match)
Now the site I have up is hacked all to hell but you can take a look at diff things you can do
http://www.gzhq.net. (i am not a guru of code)
BTW: guys and gals !!!!!!! would be very very cool to see VB as a Modual plugin to Nuke and/or make VB where it can add templates and addons to it self as a modual (like nuke).
Peace