All good advice for the why do you want to work here/for us question. Doing homework is probably placed lowest on the totem pole of priorities during the job search. Too bad because it's a huge missed opportunity on many levels. For me, knowing how the company is viewed throughout that industry is essential when deciding if it's where you want to work.
The other great benefit of doing homework to prepare for that question is telling them how great they are. Everyone likes to hear they're the prettiest girl at the party. Sharing positive information gleaned when talking to others about their experience working there, the work environment/training (whatever is your hot button) reinforces to everyone in the interview room what a great place it is to be employed.
Just my take on how to answer that question.