From the NYTimes: http://www.nytimes.com/2011/09/22/sports/for-womens-road-records-only-women-only-races-will-count.html
In short, world records for women’s road racing events are allowed only from women-only events. Men aren’t allowed. Evidently, the marathong WR is now 2:17:42, which is Paula’s third fastest time:
What is now the record — yet only the third-fastest race that Radcliffe has run — is the 2:17:42 that she ran in London in 2005. In that race, elite women started 45 minutes ahead of the men’s field, racing and finishing separately, now a common practice in major marathons.
Her 2:15:25 is now considered merely a “world best.”