url-rewriting may become 'socially unacceptable' - can anyone see that happening?
I can't! In fact, it is just now becoming mainstream with some of the more knowledgeable marketing firms.
Is google able to tell that the presented page is not the real page (eg. the http header?) and if so would they care?
Your presented page is the real page. There is no trickery here. All you are doing is rewriting the URI string so it is user friendly.
ISAPI_Rewrite is what's going to be used.
I personally highly recommend ISAPI Rewrite. There is no project too small or too large for the program. If you are familiar with writing Regular Expressions, using the program is a breeze. You just drop the .ini file in your root directory and configure from there.
They all get more listings in the SERPS and it indeed helps.
Its only natural to do the things that will make your site more user friendly. Years ago I remember seeing a handful of technical type SEOs discussing the benefits of URI rewriting. That was while ago and it still hasn't become mainstream practice. The web would be a much friendlier place if URIs were designed for usability. It would also be much more competitive! ;)