I agree, I've found through painful experience that the shiny and new, while incredibly fun, tends to cost more than it's worth.

With that said, if you're going to take the prudent route and use an established database platform, why in the name of all that is holy would you pick MySQL over Postgres?

Granted, I am rather biased, but I do have extensive experience using both in anger. Every time I have to use MySQL I walk away with the impression that it was built with the same design mentality that PHP was. The whole point of a transactional RDBMS is to keep your data as consistent and accurate as possible. I cannot in good faith use a database that (silently!) will coerce badly formatted input into what it thinks should be in the column.