It would be nice if the 7.x port had very basic gzip capability soon.
The ability to have separate path structures like it was possible in D6 wouldn't even be necessary (in the beginning). The default behavior could simply be to have an html.gz file written to the same directory for every html file, if compression is enabled.
If you're using nginx, like we are, that's all it takes to make use of its gzip_static capability. Once you turn on this setting, the server will always check for a .gz version of each file in the same directory and deliver it when the browser request suggest it can handle gz.
After all, this is also the way that the D7 core js/css aggregator is doing it.
I made a very simple mod for myself, by appending the following to boost_exit():
boost_write_file($_boost['filename'].'.gz', gzencode($data, 9));