How about Twitter? They made a product that couldn't scale, and are still doing OK. A DB server with 256GB of RAM, 2 sockets, and multiple SSD drives can serve

How about Twitter? They made a product that couldn't scale, and are still doing OK. A DB server with 256GB of RAM, 2 sockets, and multiple SSD drives can serve a lot of queries. Use that for posts, and a few slaves for reads / caching. It will cost something like $60k plus hosting fees and maintenance. But it will certainly serve 99% of web businesses as a db. As long as your basic queries scale linearly (or maybe log-linearly), you can buy your way out of the kind of trouble most web companies would kill for.