Sadly I didn't find any solutions in the biblatex doku nor in google.
Can anybody please point me out how to change the parenthesis of the authoryear-icomp (or authoryear style) from (author year) to [author year] (or recommend me another style providing that; I want to have my citations in the text in the form [author1 and author 2 year] respectively [author1 et al. year]; & instead of and would be even better)
P.S.: Does anybody know a site where I can see (I only find the styles not a printout) the different styles in comparison? Testing all of these is quite a bit of work.

doc\latex\biblatex\examplesfolder of your (la)tex installation. – Audrey Jan 21 '12 at 22:59