@akoegle - you can only push subresources (i.e. the push is tied to an existing request) - so the potential is limited. you can't just push all the files on the website hoping to seed the client's cache. (well, you can push them but the client won't use them outside of the scope of the original resource they were associated with). The client can also rst or zero-window as soon as it starts seeing data, so potential wastage is bounded (but not 0) there as well. Biggest issue is getting pushed stuff that is already cached or interferes with other stuff wanted at a higher priority; those are important and unresolved details but they shouldn't be the headline.
@teramedia - kinda like multipart, yes. but each resource has its own stream and uri so it can be addressed/reused/cached independently, as well as rejected indpendently, downloaded at different rate, etc..