MySQL is open source, highly extensible and scalable, and is available from a web interface via PHPMyAdmin, which is excellent because it's platform independent.In almost all instances that I have used MySQL, it has handled whatever I threw at it and hasn't failed me yet.
Room for Improvement:
It is a community driven project, which means that support is sometimes scarce and hard to find. Also, it really doesn't have an IDE per-se, like MSSQL does.
I use MySQL on a regular basis, specifically whenever I am managing or installing a Wordpress instance. Combined with PHPMyAdmin, MySQL is an excellent database solution for small to medium sized businesses or installations. I would recommend using a better supported database like Oracle or MSSQL for mission critical tasks on an enterprise level, but MySQL is completely capable of performing the same tasks as those other databases.