I was recently looking at Mysql's Wikipedia page. Included is a section of criticisms:
MySQL recently (2008) released version 5.1 with 20 known crashing and wrong result bugs in addition to the 35 present in version 5.0.[22] Critical bugs sometimes do not get fixed for long periods of time.[23] An example is a bug with status critical existing since 2003.[24]
MySQL shows poor performance when used for data warehousing; this is partly due to inability to utilize multiple CPU cores for processing a single query.[25]
MySQL does not offer a single table type ("storage engine") offering all features; the two most common types, MyISAM and InnoDB, do not completely overlap in their feature sets.[26]
Previous versions of MySQL did not support many standard SQL features, with the manual claiming that they were unnecessary or would hurt performance.[27] Even now, MySQL has many limitations that other RDBMS software (e.g. PostgreSQL) does not, such as the inability to refer to a temporary table twice in one query[28] and extremely poor subselect performance.[29]
The developer of the Federated Storage Engine states that "The Federated Storage Engine is a proof-of-concept storage engine",[30] though it was included and turned on by default in the main distributions of MySQL version 5.0. Some of the short-comings are documented in the "MySQL Federated Tables: The Missing Manual".
Monty's post related to all the bugs sure doesn't inspire confidence.
Also, the alphabet soup of storage engines is confusing:
Native storage engines (MyISAM, Falcon, Merge, Memory (heap), Federated, Archive, CSV, Blackhole, Cluster, Berkeley DB, EXAMPLE, and Maria)
Partner-developed storage engines (InnoDB, solidDB, NitroEDB, Infobright (formerly Brighthouse), Infobright (Open Source))
Community-developed storage engines (memcached, httpd, PBXT, Revision Engine)
Custom storage engines
Are MyISAM and InnoDB still considered the de facto storage engines?
I also noticed that PostgreSQL's page doesn't have a criticism section. Which I infer to mean it's perfect.