I am using version 0.9.1.3 with WP 3.1 and can't get minify to work. Caching is fine - but HTML minify is enabled but doesn't do anything either with disk or APC caching.
The site is http://politicalscrapbook.net/
The cache debug info appears but the minify info does not, even though both are enabled.
The wp-content/w3tc/min folder remains empty apart from .htaccess and index.php.
I haven't attempted JS and CSS minify yet.