PR up SERPS down

PR up a point dropped out of the serps though.

[recidivare]

Mature niche sport site, up until a month ago almost four figure monthly adsense earnings.

On the October trend it looks unlikely that I'll even get a check for this month. But wait there is some good news. My PR went up from 4 to 5

Am I the victim of an update thats taking it's time to sort out the SERPS or is it something deeper? I've made no material changes to the site other than the usual fresh articles.

It's only a hobby fortunately but can anyone shed some light on this?