I seem to no longer be getting email updates regarding this thread, hence my extended silence. Thanks for the heads up Ash, and for helping support others, despite their misinterpretation of your intentions and resulting accusations of hostility.
So, upgrading... I recently went through the painful painful process of upgrading a heavily customized VM 1.1.3 install to 1.1.5, and tried also at the same time to refactor out as many of the core modifications as I possibly could and instead apply them in template files, either by overriding core classes with a user_class (a great new piece of VM functionality introduced in 1.1.4) or by modifying output from core files in template files by using php output buffering. Happily, I was able to remove all core hacks, meaning that VirtueMart is much more likely to be upgradable without any special attention based on this integration, though each new version could still break something.
When I get a chance (been busy lately, so I can't promise expeditousness), I'll apply those updates I did to this integration, document the new instructions, and update the post accordingly (as well as mention the update in a new post).