I run a fairly successful adult website running on Asp.Net (c# 4.0) with a Sql Server 2008 R2 backend. We are running the free (Express) version and are getting close to our 10gb data limit. We have around 100k members and receive over 7 million page impressions (750K unique visitors).
I'm looking at free (or cheap) alternatives as we cannot afford the USD$7K+ that Microsoft are charging for their processor license for the standard edition. There's not much hope of us getting a free license either on their biz spark program!
We have a fairly typical schema for any membership database. We are moving towards a more social aspect, so think of an adult Facebook. We currently have 42 tables in our database. I'm conscious of the issues of scale. We have been growing at a drastic rate so are considering a NoSql alternative.
So, I'm considering Postgres and RavenDB. Postgres would have the least amount of friction in terms of code change and data migration. However, if we were to become Facebook (lolz) then I would end up writing the data layer again (which makes me sad).
So maybe start out now with a NoSql solution such as RavenDb or Mongo which has sharding built in.
Thoughts?
Go to Postgres right now, and tackle the growth problem when you actually outgrow Postgres.
You have to pick your battles in this business and premature optimization is one of the best ways to waste resources in software development.