Currently, latexsearch.com uses the content available from Springer's corpus of literature, but future development plans include expanding this content set to include open-access databases and preprint servers such as ArXiV. Anyone who would like to assist us in expanding the content base of latexsearch.com is encouraged to contact us.

Anyone is very welcome to discuss incorporating the MathOverflow corpus. It's all available in a convenient format in the public database dumps, and the license is certainly permissive enough for them to index MO this way.

On the other hand, it's Springer...

As to the LaTex I arbitrarily took to demonstrate what I meant, I took it from here: http://mathoverflow.net/questions/47870/does-a-triangulated-category-that-possesses-a-subcategory-b-of-generators-with

We have no ability to modify the software at present, beyond reporting critical bugs to the StackExchange folks. If we ever transition to StackExchange 2.0, we will gain lots of new software features (but not, at present, such searching), and at least some ability to petition the developers for particular new features. In the 2.0 model, however, software features which are not useful to all the StackExchange sites are very unlikely to be implemented. There's a dim possibility that at some point we'll have our own software --- I've continued intermittent work on alpha.mathoverflow.net, although there's currently no publicly accessible instance, and perhaps in a few months I'll have something that others can usefully contribute to.

That said, have you tried google? I didn't find anything for the particular LaTeX fragment you mentioned (did you actually get that from an existing post?), but otherwise it seems to pretty successfully find LaTeX fragments.