I hadn't heard of this site before: http://db-engines.com/en/ but it seems they
maintain rankings of various database-related applications based on keyword
popularity, frequency of job offers etc. It seems PostgreSQL has just overtaken
MS Access to climb to 4th place:
http://db-engines.com/en/blog_post/10
The methodology looks like it produces a useful overview of general trends,
although with this kind of thing I guess the actual "scores" produced are
pretty meaningless.
http://db-engines.com/en/ranking_definition
Full list here:
http://db-engines.com/en/ranking
Regards
Ian Barwick