I have already taken the "plunge" to nginx, and my findings:
.htaccess rules are one of the main problems, but can be overcome by
"translating" them to nginx configuration instructions (you can do
them by hand, but there are some handy tools on the internet to help
you convert them, like this one: htaccess to nginx converter)
Note that in some cases having an .htaccess with certain rules (which
nginx will ignore) will break the site! (nginx ignores it, but
somehow it breaks it (giving an error 500)). This has not happened to
the stock .htaccess from Joomla.
Virtual hosts are managed in a different way (not really related to
Joomla, but still important to know)
It is indeed very fast! I compared to the same site with an Apache
Other than that I haven't found any other problems.
EDIT: some aditional input about the extensions:
All the stock extensions work as expected
The URL rewriting and SEO works as expected (as long as you define
the rules in nginx)
Other extensions work as expected, the ones I tested are:
Akeeba Backup (latest); JCE (latest); Community Builder (latest); Chronoforms (latest)
Even my customized extensions (created by myself) work without any
This was with two sites (the technical details are Joomla 3.2.2, nginx/1.1.19, PHP 5.4.25 (FPM), mySQL 5.5.35, Ubuntu 12.04.4).
The bottom line is that in my tests and production sites, all is working fine and not that hard to set up and run, so go for it!