Just when it looked like the red queen hypothesis was gaining the upper hand as an explanation for the prevalence of sex across the animal and plant kingdoms it has started to struggle to explain why species have so much sex. Why not reproduce asexually most of the time to get the benefits of that strategy and throw in a little sexual reproduction here and there for variety (literally)?
There's a nice essay by Matt Ridley on the PBS Evolution website that discusses the issues. The website has some nice resources apart from this.
Here's a BBC report from a paper in 2004 which takes the issue further and asks whether the Red Queen hypothesis can really explain why we have so much sex...
And to bring us up to date here's a link to a report on a paper from 2006 that argues that the Red Queen hypothesis does just fine if we take into account the maternal transmission of parasites.