O'Reilly did a series of brief profiles of how different fairly well-known companies have tackled the problem.
[link|http://radar.oreilly.com/archives/2006/04/web_20_and_databases_part_1_se.html|http://radar.oreilly...es_part_1_se.html]
[link|http://radar.oreilly.com/archives/2006/04/database_war_stories_2_bloglin.html|http://radar.oreilly...es_2_bloglin.html]
[link|http://radar.oreilly.com/archives/2006/04/database_war_stories_3_flickr.html|http://radar.oreilly...ies_3_flickr.html]
[link|http://radar.oreilly.com/archives/2006/04/database_war_stories_4_nasa_wo.html|http://radar.oreilly...es_4_nasa_wo.html]
[link|http://radar.oreilly.com/archives/2006/04/database_war_stories_5_craigsl.html|http://radar.oreilly...es_5_craigsl.html]
[link|http://radar.oreilly.com/archives/2006/05/database_war_stories_6_oreilly.html|http://radar.oreilly...es_6_oreilly.html]
[link|http://radar.oreilly.com/archives/2006/05/database_war_stories_7_google.html|http://radar.oreilly...ies_7_google.html]
[link|http://radar.oreilly.com/archives/2006/05/database_war_stories_8_findory_1.html|http://radar.oreilly..._8_findory_1.html]
[link|http://radar.oreilly.com/archives/2006/05/brian_aker_of_mysql_responds.html|http://radar.oreilly...sql_responds.html]
An interesting series of reads. The comments are worth reading as well.
Cheers,
Ben