This week's New Media Age has a great feature on blogging. Two pieces actually.
Top tip from UK digital agency Hyper Happen (they're all over it): if it's technology, trend, entertainment or fashion led, it needs to be blogged. If it's a cleaning product, don't bother! (reference to the Cillit Bang blog PR programme that went disastrously wrong when Cohn & Wolfe PR reportedly started splogging in completely inapropriate blogs - like here - not pretty reading).