There are any number of reasons why the Less Wrong crowd might be interested in mindfulness meditation.  Cultivating an ability to observe thoughts without being swept away in them could help in noticing when you're confused, looking into the dark, and, if you are skilled enough, actually changing your mind.  I've been on a couple of retreats myself, and I value meditation because it's a useful technique with a lot of field testing that can be studied free of the religious context it generally comes packaged in. The results have been positive -- I've learned what a mess my mind really is and my metacognitive awareness has improved noticeably.

Recent research suggests that we can add improved cognitive functioning to the list (Mrazek et al., 2013).  

There is no shortage of researchers and individuals interested in better thinking, and perhaps the most effective way of doing so is to "target a cognitive process underlying performance in a variety of contexts".  A great example of such a process is "the ability to attend to a task without distraction", as unrelated thoughts compete with the job at hand for limited working memory. Based on this it makes sense to hypothesize that, if mindfulness training can reduce mind-wandering and distractedness, it ought to boost mental performance.  

Psychologists at the University of California Santa Barbara examined this hypothesis using a test of reading comprehension and a test of working memory capacity.  Forty eight subjects, all undergraduates, were given two tasks: one, a modified version of the GRE verbal section and two, a test of working memory called the operation span task.  The verbal section simply had all the vocabulary questions removed, while the operation span task alternates something that must be memorized (like a letter) with something irrelevant (like an equation which must be evaluated as true or false).  If compared to someone else you can hold a longer string of memorized letters in your mind while also accurately evaluating equations, then you have a better working memory.  

Importantly, during these tasks a couple of different techniques were used to assess mind-wandering, including asking subjects to assess themselves after the fact and asking them semi-randomly during the task.  

Then the subjects were divided into a group which attended a two-week class on nutrition and a group which attended a two-week class on mindfulness meditation.  Meditation instruction was pretty straightforward: 

"Each class included 10 to 20 min of mindfulness exercises requiring focused attention to some aspect of sensory experience (e.g., sensations of breathing, tastes of a piece of fruit, or sounds of an audio recording)...Classes focused on (a) sitting in an upright posture with legs crossed and gaze lowered, (b) distinguishing between naturally arising thoughts and elaborated thinking, (c) minimizing the distracting quality of past and future concerns by reframing them as mental projections occurring in the present, (d) using the breath as an anchor for attention during meditation, (e) repeatedly counting up to 21 consecutive exhalations, and (f) allowing the mind to rest naturally rather than trying to suppress the occurrence of thoughts.

Two-weeks later, the groups were tested again and it was found that:

relative to nutrition training, which did not cause changes in performance or mind wandering, the mindfulness training led to an enhancement of performance that was mediated by reduced mind wandering among participants who had been prone to mind wandering at pretesting. 

I couldn't help but wonder about how much of a positive effect could be had by someone who didn't actually do the meditation. An interesting additional experiment to have done would've been explaining (b) and (c) (in the first block quote) to participants, asking them how much their minds wandered semi-randomly during a task and then after a task, and testing them again two weeks later.  Is noticing the problem enough to get a partial solution, or does flexing your attention add something that you can't get any other way?  

This is good news for those of us who would like to get the most out of our brains in an age before really high-octane cognitive enhancements are available.