I doubt very much. They're basically using Redis as a much more powerful memcached. SQL Server still is the ultimate owner of all StackOverflow data, last time I talked to the team.
I was also wondering if they'd developed any generic custom code to fetch from Redis or fetch from SQL/insert into Redis, and how it fits into their application logic. (e.g. does it happen before they make a LINQ to SQL query, or does it intercept LINQ to SQL queries and return results from Redis).
With downloads for windows: https://github.com/dmajkic/redis/downloads
Here's an example of an OSS 1-page mini-StackOverflow, written only using Redis: http://www.servicestack.net/RedisStackOverflow/
And this page has caching web services examples (at the bottom), with source code of non-non-invasively dropping in a Redis cache provider using an IOC.
http://www.servicestack.net/ServiceStack.Northwind/
If you want to learn more about Redis, here is an article on how to build an application using only POCO's and Redis: https://github.com/ServiceStack/ServiceStack.Redis/wiki/Desi...
With more info on the wiki: https://github.com/ServiceStack/ServiceStack.Redis/wiki/Desi...