Nginx runs all my Rails sites and will forever. If you haven't tried it yet, I can't say enough good things about it. It never breaks. It has just absurdly good memory consumption, which is clutch when you're trying to run your site on a memory heavy platform like Rails on a VPS which is very memory constrained.

(By comparison, Apache is quite the memory hog and I still haven't figured out how to say the magic words to get it to not effectively crash my blog and every other site on the server if I burst to 10,000 visitors in an hour. That is not supposed to be a big number. Apache has 500 MB to play with and still can't keep up.)

I also find, and this might just be a matter of taste, that the configuration makes more sense to me than Apache configuration does. This is funny because Apache configuration is obsessively well-documented and Nginx configuration is not.

Additionally, some easy-to-use features cover weak points in typical Rails (&etc) deployment scenarios. The big one for me is file serving, since my website is essentially one big PDF printing press. The simplest level (works for me, won't work for Facebook) is just having the file anywhere accessible on the disk and having the application put a special header on the response saying "Hey, Nginx: give them this path.", then terminating Rails' involvement. That frees up your Mongrel to start doing hard work again and greatly, greatly, GREATLY decreases the resources you need to stream your 5 MB PDF, 20 MB executable, etc to the user.

So it scales down, but does it scale up? Ooooooooh yeah. Impressively so. See the tales of Wordpress deployment, where not a whole lot of Nginx gets hit with a year's worth of my traffic every couple of seconds and still keeps on trucking.