:^)It just made my whole day. I kept spitting coffee out everywhere I was laughing so hard. I guess I was lucky registering with my Yahoo account.
1. It's not really designed for static content. The help files suggest differently!It probably will not have the same performance improvement as for a cached report, chart or a dynamic PL/SQL region. But I think there are still a little performance gain. Why? It doesn't have to look for substitution, doesn't have to merge it with the template, ... If you can cache a hole page which just contains static content like navigation, lists, ... you should also see an improvement, because APEX doesn't have to loop though all it's meta-data to build the page.
2. If I set page 0 (or regions on page 0) to cache, will this automatically cache those shared regions on other pages?Yes they will be cached there too.
3. If I set a page to cache, will the regions cache automatically or are their settings independent.If you set a page to cached, the whole page is in the cache. It will not look at the individual regions anymore if it finds the page in the cache.
4. If I set a region to cache that contains a paginated report, how does that work? And will it conflict with PPR?Caching for a region is ignored if the REQUEST is set. If you do pagination, you will see that this request is always issued with a request that contains the report region (eg.: pg_R_4177313812138401049)
5. If you set the application to cache lots of data, by user; and you have a lot of users; is there an impact elsewhere?It depends if you are doing the caching "By User" or "application wide". There are reports available which show you the bytes used by the cached pages/regions => Application Reports/Activity/Cache*