I think it's a cat and mouse game. The more that Linkedin publishes about their anti-spam techniques, the more information spammers have to try to evade those anti-spam techniques.
If you're interested in these sorts of micro-optimizations, you may find Mozilla's nsTArray (essentially std::vector) interesting.
One of its unusual design decisions is that the array's length and capacity is stored next to the array elements themselves. This means that nsTArray stores just one pointer, which makes for more compact DOM objects and so on.
To make this work requires some cooperation with Firefox's allocator (jemalloc, the same one that FB uses, although afaik FB uses a newer version). In particular, it would be a bummer if nsTArray decided to allocate space for e.g. 4kb worth of elements and then tacked on a header of size 8 bytes, because then we'd end up allocating 8kb from the OS (two pages) and wasting most of that second page. So nsTArray works with the allocator to figure out the right number of elements to allocate without wasting too much space.
We don't want to allocate a new header for zero-length arrays. The natural thing to do would be to set nsTArray's pointer to NULL when it's empty, but then you'd have to incur a branch on every access to the array's size/capacity.
So instead, empty nsTArrays are pointers to a globally-shared "empty header" that describes an array with capacity and length 0.
Mozilla also has a class with some inline storage, like folly's fixed_array. What's interesting about Mozilla's version, called nsAutoTArray, is that it shares a structure with nsTArray, so you can cast it to a const nsTArray*. This lets you write a function which will take an const nsTArray& or const nsAutoTArray& without templates.
Anyway, I won't pretend that the code is pretty, but there's a bunch of good stuff in there if you're willing to dig.
