[ Moderator note: post and link fixed. ]
JetPack does not work for me in my .org instance but now I know why. Rather than rehash a long discussion I had on the .com JetPack forum, please read this:
Now that we are on the same page, the JetPack implementation for .org is brain dead. Most folks, me included, will run a dev server behind a firewall and thus make that platform inaccessible as a server to the cloud. Yes, it is a server but it's meant to be used internally, on an Intranet. My implementation is inside MAMP on my Mac so the server is localhost. I would no more make my Mac visible to XML-RPC than I would ftp nor would I make a Linux dev server visible if I chose that platform for LAMP. I think Automattic needs to rethink JetPack.
As to diffs between WP LaTeX and JetPack, I never got Beautiful Math to work because of that XML-RPC issue. I was able to activate JetPack but many modules, including Beautiful Math were unavailable. They do not offer the activate/deactivate buttons without a working XML-RPC service. The diffs between WP LaTeX and WordPress.com LaTeX, which I assume is a superset of what's in JetPack, are minor but annoying. In WP Latex we can use the short code to say [latex size="-1"]my LaTeX expression[/latex]. In .com we have to say... $latex my LaTeX expression&s=-1$. You just have to be aware of this and add the extra step after the paste.
I have not tried LaTeX in a comment, only in posts.
It must be obvious from what I wrote in the .com piece that I am not a fan of generating .png image files to render LaTeX. I'm now using MathJax-Latex and it is doing what I want it to do. Remember too, I may never deploy a .org version of WordPress. Mine is as a sandbox to better understand the WordPress platform. I wanted access to the php code and the only way to get it is to run a .org sandbox. I think the .png approach was correct before browsers were made smart with the inclusion of LaTeX rendering engines. Can you still make a case for a .png design? Which approach would you say is best for mobile devices? And message to you too, as I said to the JetPack audience, you could make WP LaTeX rally smart and inspect the browser before deciding whether to send a .png or let the browser do the rendering.
Man, LaTeX is such an interesting notion. I really enjoyed hacking it and discussing it.