About the localization of a UFD 
I was wondering, is the localization of a UFD also a UFD? 

How would one go about proving this? It seems like it would be kind of messy to prove if it is true.
If it is not true, what about localizing at a prime? Or what if the UFD is Noetherian?

One slick way is via Kaplansky's characterization: a domain is a UFD iff every nonzero prime ideal contains a nonzero prime. This is easily seen to be preserved by localization, hence the proof. Alternatively, proceed directly by showing that primes stay prime in the localization if they survive (don't become units). Thus UFD localizations are characterized by the set of primes that survive.
The converse is also true for atomic domains, i.e. domains where nonzero nonunits factor into atoms (irreducibles). Namely, if $\rm\:D\:$ is an atomic domain and $\rm\:S\:$ is a saturated submonoid of $\rm\:D^*$ generated by primes, then $\rm\: D_S$ UFD $\rm\:\Rightarrow\:D$ UFD $\:\!$ (a.k.a. Nagata's Lemma). This yields a slick proof of $\rm\:D$ UFD $\rm\Rightarrow D[x]$ UFD, viz. $\rm\:S = D^*\:$ is generated by primes, so localizing yields the UFD $\rm\:F[x],\:$ $\rm\:F =\,$ fraction field of $\rm\:D.\:$ Thus $\rm\:D[x]\:$ is a UFD, by Nagata's Lemma. This gives a more conceptual, more structural view of the essence of the matter (vs. traditional argument by Gauss' Lemma).
