I am using a nonstandard citation format, primarily for simplicity.  An example is:

MathOverflow Questions (Number refers to URL, so 37679
expands to "http:// mathoverflow.net/questions/37679") [Note: the current display scripts
replace the URL with a visible title and hidden link: I've added a space to break this feature.  My actual example would not have the space.]

88323 Analogues of Jacobsthal's Function. 

56099 Lower bound of the number of relatively primes (each other)
in an interval. 

68351 Least Prime Factor in a sequence of 2n consecutive integers. 

Since I am not interested in making changes when URLs change or databases change,
I prefer to provide a simple recipe for translation to avoid as few broken links as possible.  I also let the user grab the date from the paper or its metadata, so they
can provide their context.  

If I were to improve upon this, I might add something like "at this writing 2014.03",
as well as provide links to specific versions of the post as suggested by quid.  I
would refrain from referring to something more specific than the post and its answers;
if I had to, I would craft a similar recipe, such as:(Number;version refers to
URL, so 37679;38690/1 refers to http://mathoverflow.net/revisions/37679/38690/1).
The rationale for this is to give a simple recipe that works at the time the document
was publicized, and let the future researcher modify the recipe as needed to resolve the
references.  If I have to change anything, I only need to change the recipe, not all
of its occurrences, unless the question numbering changes.

Gerhard "Prefers Simplicity, Replicability Over Ultra-convenience" Paseman, 2014.04.17