I'm reading this series right now - well, I've just finished the fourth book and I'm waiting for the fifth, sixth, seventh, and eighth to be delivered. Personally I find the series ok-ish but I've found some of the actions of the characters are annoying. I agree with Debbie that they are probably likely to get more boring as I read more of them.
Not my favourite series certainly, but they're quite good and I'll definatly have to finish reading them all; if just to find out what happens.