I wrote some long posts about
daemon cost effectiveness,
daemon characters and also
magic lores. There is tons of stuff to read there so if you want to have quick review then link that Talonz provided has some good musings about what we got.
Daemons still do trash and dominate many tournaments, but since sadistic comping system has spread in many countries, daemons are restricted harslhy in those and it ofcourse affects our gameplay. Though even with heavy comps daemons are still very strong top tier army.
Short recap of what has been discussed are things like: Seekers, beasts and Princes are useless. Screamers can be good sometimes, but are very unreliable. Fleshhounds are underappreciated and are actually quite nice. Core daemons, fiends, flamers and Greater daemons rock the world and are all very strong. If you can specify what kind of information you are seeking then we could provide some more of it

And welcome back =)