Most of the servers are workers which fetch feeds. Parallel downloads across a number of low-level commodity servers. Additionally, there's a master and slave Postgres database, a small Cassandra cluster, 2 redis boxes, an elasticsearch cluster, front-end servers, caching servers, etc. Shoot me an email if you want to talk in more detail.
One server to serve an RSS reader to the 5k users, 23 others to host 23 different stats and monitoring applications to make sure that one server is working OK?
I recently tried to teach myself F#. Although the community is very small compared to others, the folks I ran into were warm and enthusiastically helpful.
Most of the intro texts I tried were not good. I found a fantastic one, but it is an outdated, abandoned text that must be accessed through the Internet Archive [1]. I tried to contact the authors to see if I could help updating it, but received no response.
The language has a large surface area. It is not uncommon to think you have learned a lot of F#, then read a blog post by someone full of F# code and think "what the heck is that symbol?"
I agree with others that note the MS influence. Things are definitely getting better, but you will have an easier time if you are in the MS ecosystem.
For what it's worth, I wrote a blog post [2] that might be helpful if you're trying to get started.
http://fsharp.org and Scott's site are the go to sites for all things F#. The Twitter hashtag #fsharp is sure to get you retweeted and/or responded to, and finally any well-formulated question to stackoverflow with an F# tag will get a speedy response.
