First of all, according to this answer, the :cache => true option on stylesheet_link_tag and javascript_include_tag doesn't work on Heroku. Is this true? I've found :cache => true to work occasionally, but not always (weird!)
Also, what's the best solution here? Ideally it would seamlessly combine and minify all CSS / JS. Heroku Asset Packager claims to do this -- are there better options?
GitHub has a good answer for this, and I'm sure you could modify Heroku's deployment scripts to integrate:
http://github.com/blog/551-optimizing-asset-bundling-and-serving-with-rails
I haven't tried it on heroku yet, but Sprockets might be good for that. Also, in the past, I've had more luck with
:cache => 'all.css'
:cache => 'all.js'
instead of 'true'
It's a different way to manage your CSS/Javascript but you may want to check out the Rails plugin shoebox.
Shoebox can do combining, minifying, and caching.