I've posted this to the issue tracker but I suspect that it might not be an "issue" but just something I'm missing, so just in case, let me ask here.
There is a LESS plug-in for PhpStorm that comes bundled. *.less files are indeed recognized, in that a little "LESS" icon appears next to the *.less files, but it appears that the "support" ends there. Code completion (with Ctrl-SPACE) does not work for me as it does for *.css files. I assume it's supposed to right? Is there some place in the Settings that I need to enable code completion for less files?
I'm using PhpStorm 2.1.4.
As I said, I posted this to the issue tracker so please vote it up if you also have this problem.
Also, I posted a question about it on StackOverflow with little luck so far.
Unfortunally at the moment LESS code completion is not available because of the CSS support internal changes, and we haven't adopted LESS support yet, however this is our high priority task on the list for RubyMine next version (as far as LESS support is being developed by RubyMine team), and for PhpStorm.
Sorry for inconveniences.