Seen lots of posts/talks about best practices of writing sass lately.. I feel like some of these could be codified and presented in compass to enforce these improvements better than a smattering of external posts.
Actually, compass 0.12 shows both sass and css filesize in the stats output.
One idea is that just printing the css filesize when compiling might actually have a dramatic end-user behavior effect (like showing the runtime gas mileage in a car).
We could also have a strict mode that would forbid certain bad behaviors like nesting more than 4 levels deep.
gzipped filesize would be better as it wipes out the cost of vendor prefixes, among other things. see also @necolas's latest post about CSS and gzip.
I've thought about using sparklines to indicate filesize growth over time.
Strict mode is a good idea, yeah.
At my company, we have two callbacks in our config.rb: one that outputs the file size (normal and gziped) and one that outputs the selector and property count (and outputs a warning, if properties are above 4096 for IE -> see blesscss)
https://gist.github.com/2164668 (I am no ruby programmer... the selector count callback looks a bit hacky :P )
We just add this to every config.rb of our projects
(another callback is for generated sprites: it calles imgopt/optipng on the generated sprites)
BTW, the 4096 IE bug for the number of rules.