Applications of the notion of of Gromov-Hausdorff distance I am looking for applications of the notion of Gromov-Hausdorff convergence to prove theorems that a priori have nothing to do with it. Examples that I am aware of (thanks to wikipedia and google):

*

*Gromov's theorem


*The Wikipedia page links to a paper that uses GH convergence to prove a stability result in cosmology.
What are more examples? Ideally they would be along the lines of Gromov's theorem, or proofs of geometric facts, but I'm interested to hear about anything.
As a subquestion, are there interesting applications of Gromov's compactness theorem to prove results about manifolds with bounded Ricci which have nothing to do with GH convergence?
 A: The scaling limits of several families of random graphs are shown to exist by using the idea of Gromov-Hausdorff convergence to certain random metric spaces.  
For instance, uniformly chosen triangulations of the sphere with $n$ faces endowed with the graph distance have been proved to converge (in the Gromov-Hausdorff sense) after rescaling distances by $n^{-1/4}$ to a particular random metric space called the Brownian map.  See the references in this earlier answer of mine. 
A: Another graph-theoretic application.
Given an undirected finite graph $G$, the Colin de Verdière graph invariant $\mu(G)$ is defined as the maximum multiplicity of the second smallest eigenvalue of a matrix $M\in O_G$, provided that this eigenvalue is structurally stable. Here, $O_G$ is an interesting (for $G$) subset of the symmetric matrices called the  Schrödinger-like operators on $G$.
It turns out that this invariant is very nice in the following sense: if $H$ is a minor of $G$, then the invariant verifies $\mu(H) \leq\mu(G)$. A trick used to prove this result is to put weights on the edges of $G$ to turn it into a metric space (with the obvious distance of smallest sum of weight in a path). Then, any minor $H$ can be obtained as a Gromov-Hausdorff limit of $G$ with suitable weights (contracted edges see their weight go to zero and deleted edges have their weight go to infinity), and conversely, any sequence of weights on the edges of $G$ that converges gives a minor.
Now that I wrote it down, it does not seem like such a powerful remark, but, as I recall, this shift in point of view is (at the very least) very convenient to prove the result.
A: Stephen Keith used the Gromov-Hausdorff convergence to study the existence of (measurable) differentiable structure on metric measure spaces that supports a Poincare inequality or K-Lip-lip condition.
Juha Heinonen, Jeff Cheeger and Stephen Keith also used this method as a standard blow up argument in related questions.
Heinonen, Juha; Keith, Stephen Flat forms, bi-Lipschitz parameterizations, and smoothability of manifolds. Publ. Math. Inst. Hautes Études Sci. No. 113 (2011), 1–37.
Keith, Stephen A differentiable structure for metric measure spaces. Adv. Math. 183 (2004), no. 2, 271–315.
J. Cheeger, Differentiability of Lipschitz functions on metric measure spaces, Geom. Funct. Anal. 9 (3) (1999) 428–517.
J. Cheeger, T.H. Colding, On the structure of spaces with Ricci curvature bounded below. I, II, III, J. Differential Geom.
A: Facundo Memoli applied Gromov-Hausdorff distance to shape matching in his Ph.D. thesis.
http://math.stanford.edu/~memoli/research.html (Wayback Machine, new website)
A: Gromov's Theorem was, as far as I'm aware, the first but very far from the last application of Gromov–Hausdorff distance to group theory.  One particularly fruitful line of reasoning starts with a sequence of actions of a group $\Gamma$ on (Gromov)-hyperbolic metric spaces. In the (rescaled) limit, one gets an action on an $\mathbb{R}$-tree, to which one can apply Rips' structure theory.
Examples include:

*

*Bestvina's construction of a boundary for the set of hyperbolic structures on a manifold;

*Paulin's Theorem: if $\Gamma$ is word-hyperbolic and $\mathrm{Out}(\Gamma)$ is infinite then $\Gamma$ splits over a virtually cyclic subgroup;

*Sela's theorem that word-hyperbolic groups are Hopfian;

*this idea is the principal tool in Sela's solution to Tarski's Problem on the elementary theory of free groups;

*etc.

A: Gromov-Hausdorff convergence (with basepoints) is used quite a bit in the classification of Kleinian groups. In particular, it is used to resolve the Ahlfors measure conjecture and the ending lamination conjecture. It is also used in the proof of the geometrization conjecture (and as a corollary the Poincare conjecture).
A: Many people have applied Gromov-Hausdorff convergence to obtain information about Riemannian manifolds with nonnegative Ricci curvature.  Controls on Gromov-Hausdorff limits can lead to controls on diameters.  For example in my thesis I proved, among other things, that manifolds with nonnegative Ricci curvature and linear volume growth have sublinear diameter growth.  The proof uses Gromov-Hausdorff convergence and methods of Cheeger-Colding to obtain that convergence.  
Other times Riemannian geometers use Gromov-Hausdorff convergence to come up with an idea but later simplify the proof in a way which circumvents actually mentioning the Gromov-Hausdorff convergence.  I have a paper about fundamental groups of manifolds with nonnegative Ricci curvature and my original proof of the main theorem involved taking a Gromov-Hausdorff limit (as described in the final section of the paper).  Then I thought of a simplification which allows one to obtain the main theorem without appealing to Gromov's compactness theorem.   
A: For another kind of answer, there are some papers using Gromow-Hausdorff distance in applied mathematics, for instance, shape modeling:  https://graphics.stanford.edu/courses/cs468-08-fall/pdf/dghlp-pbg.pdf
or in topological data analysis:  https://www.fields.utoronto.ca/talk-media/1/26/87/slides.pdf
