If you anticipate having to write a report, obviously you should use the right tool. If you don't, use what's simple and gets the job done. It's not incredibly

If you anticipate having to write a report, obviously you should use the right tool. If you don't, use what's simple and gets the job done. It's not incredibly hard to switch later. On the low-end, administration for MySQL is certainly not easy; for an app you build in a day or two on Rails or Django or Sinatra (or as a CLI tool for that matter) you can easily spend more time doing sysadmin work to provision, configure and maintain MySQL than you do writing software. (MySQL shared hosting isn't everywhere.) There are plenty of throwaway webapps out there that just aren't worth setting up a database server for. On the high end, it's not a matter of what's easy; it's a matter of what's possible. These are different use cases, and there are different software packages being advocated for them. No one who needs a disk-backed hash table is using Hypertable, and no one who needs massively parallel analytical capability is using Tokyo Cabinet. And no one's advocating reconsidering RDBMS use as a whole; just RDBMS use as the default choice.