The other day i was watching video clip of Darren of Problogger answering a question that if Maintaining Two blogs at 50% efforts are more worth than maintaining one blog at 100% effort. Both techniques of blogging have its advantages and disadvantages.
However for Newbies who are just getting into blogging in my experience should concentrate one blog with 100% effort. Because the initial stage of the blogging career for problogger is the toughest part. Maintaining two blogs at an early stage could lead both of your blog to failure.
Nevertheless you can run more than one blog successful blogs once you already have one established blog with good number of readers and down the road you also run various tricks to promote and gain readership quickly. And another advantage of having more than one more blog is that it would enable you cover other topics that you could not do previously hence increasing your readership even more. Again, at an early stage just focus on One blog and put your 100% effort to it. Else there is higher possibility that you could not succeed with any of them.