In the LabVIEW community a phrase that has been used to describe undocumented, or incomplete features of LabVIEW has at times been called Rusty Nails. In searching LAVA it appear this is never explained and so this post is intended to give a brief history with as many details as I know having not been active when this all took place.
The earliest reference to "Rusty Nails" found online (thanks to AQ) is by Greg McKaskle of NI in 1999. Someone was asking about all the undocumented INI settings that could be found, and how some weren't exposed to the Tools >> Options dialog. Greg's reply was this:
Back in the LabVIEW 5.x and 6.x era there was a new emerging technology that was LabVIEW Scripting. NI had created scripting for their own purposes but the community saw it and wanted to be able to automate editing, or creating LabVIEW code. With the help from Jim Kring and others, the basic tools for enabling scripting in LabVIEW were available. The story of how this came about is worth a post of its own, but the summary is that NI shipped a VI that didn't have a password on the block diagram, which allowed for the creation of any object, given an ID. Using a for loop, you could easily create every object in LabVIEW, including objects which facilitate in creating and manipulating code. Discussing scripting often leads into discussing other INI keys which enable private functions like the well known SuperSecretPrivateSpecialStuff. It is possible this is one of the keys Greg was referring to. Other INI keys from 5.x can be found here.
After these discoveries the NI forums started getting users asking about scripting, and private functions. Users were looking for help, and documentation but NI wasn't ready for this knowledge to be public and so they started deleting all posts related to private, and scripting functionality. Some of the motivation for the creation of LAVAG came about by a desire to have an independent place to discuss the LabVIEW topics that NI didn't want to have on the public forums, potentially adding to the number of support calls, and confusing new users with advanced topics that were undocumented or incomplete.
After LAVA's creation a subforum section was labeled Rusty Nails, and intended to be a place to discuss Scripting, ExternalNodes, XNodes, Private methods, and general LabVIEW hackery. Over the years several private functions have been made public, and scripting has become an official feature shipping with LabVIEW. Because of this the Rusty Nails and XNodes subforums were combined into what is now the VI Scripting section. Even over on the official NI forums, discussions about private functionality and XNodes has been relaxed since those early days. Asking for private methods and getting unofficial help is something users, and sometimes NI employees will participate in, without the heavy censorship seen earlier. And topics of scripting are encouraged now that the feature has been official since LabVIEW 8.6.
If you have anything you'd like me to add regarding scripting's history feel free to reply and I can add it. And if I got any of the details wrong let me know. Again I wasn't around when this all took place and I've just tried putting down the details I've heard from other developers.